Cytochrome-c oxidase deficiency is a genetic disorder that affects the function of the mitochondria, which are the energy-producing structures in cells. Specifically, it is a deficiency in cytochrome-c oxidase (COX), also known as complex IV, which is an enzyme located in the inner membrane of the mitochondria that plays a critical role in the electron transport chain and oxidative phosphorylation.

Cytochrome-c oxidase deficiency can be caused by mutations in any of the genes that encode the subunits or assembly factors of COX. The severity of the disorder and the specific symptoms can vary widely, depending on the extent of the enzyme deficiency and the particular tissues and organs that are affected.

Symptoms of cytochrome-c oxidase deficiency may include muscle weakness, developmental delay, hypotonia (low muscle tone), seizures, lactic acidosis, and cardiac and neurological problems. In some cases, the disorder can be life-threatening in infancy or early childhood.

There is no cure for cytochrome-c oxidase deficiency, and treatment is generally supportive and aimed at addressing specific symptoms. Antioxidant therapy, such as vitamin C and E supplements, may help to reduce oxidative stress and improve mitochondrial function in some cases. In severe cases, a heart or liver transplant may be considered.

Leigh Disease, also known as Subacute Necrotizing Encephalomyelopathy (SNE), is a rare inherited neurometabolic disorder that affects the central nervous system. It is characterized by progressive degeneration of the brain and spinal cord. The condition typically appears in infancy or early childhood, although it can develop in adolescence or adulthood.

Leigh Disease is caused by mutations in mitochondrial DNA or nuclear genes that disrupt the function of the oxidative phosphorylation system, a part of the cellular energy production process. This results in decreased ATP (adenosine triphosphate) production and an accumulation of lactic acid in the body.

The symptoms of Leigh Disease can vary widely but often include vomiting, seizures, developmental delays, muscle weakness, loss of muscle tone, and difficulty swallowing and breathing. The condition can also cause lesions to form on the brainstem and basal ganglia, which can lead to further neurological problems.

There is no cure for Leigh Disease, and treatment is focused on managing symptoms and supporting affected individuals as they cope with the progression of the disease.

Electron Transport Complex IV is also known as Cytochrome c oxidase. It is the last complex in the electron transport chain, located in the inner mitochondrial membrane of eukaryotic cells and the plasma membrane of prokaryotic cells. This complex contains 13 subunits, two heme groups (a and a3), and three copper centers (A, B, and C).

In the electron transport chain, Complex IV receives electrons from cytochrome c and transfers them to molecular oxygen, reducing it to water. This process is accompanied by the pumping of protons across the membrane, contributing to the generation of a proton gradient that drives ATP synthesis via ATP synthase (Complex V). The overall reaction catalyzed by Complex IV can be summarized as follows:

4e- + 4H+ + O2 → 2H2O

Defects in Cytochrome c oxidase can lead to various diseases, including mitochondrial encephalomyopathies and neurodegenerative disorders.

Lactic acidosis is a medical condition characterized by an excess accumulation of lactic acid in the body. Lactic acid is a byproduct produced in the muscles and other tissues during periods of low oxygen supply or increased energy demand. Under normal circumstances, lactic acid is quickly metabolized and cleared from the body. However, when the production of lactic acid exceeds its clearance, it can lead to a state of acidosis, where the pH of the blood becomes too acidic.

Lactic acidosis can be caused by several factors, including:

* Prolonged exercise or strenuous physical activity
* Severe illness or infection
* Certain medications, such as metformin and isoniazid
* Alcoholism
* Hypoxia (low oxygen levels) due to lung disease, heart failure, or anemia
* Inherited metabolic disorders that affect the body's ability to metabolize lactic acid

Symptoms of lactic acidosis may include rapid breathing, fatigue, muscle weakness, nausea, vomiting, and abdominal pain. Severe cases can lead to coma, organ failure, and even death. Treatment typically involves addressing the underlying cause of the condition and providing supportive care, such as administering intravenous fluids and bicarbonate to help restore normal pH levels.

Mitochondrial proteins are any proteins that are encoded by the nuclear genome or mitochondrial genome and are located within the mitochondria, an organelle found in eukaryotic cells. These proteins play crucial roles in various cellular processes including energy production, metabolism of lipids, amino acids, and steroids, regulation of calcium homeostasis, and programmed cell death or apoptosis.

Mitochondrial proteins can be classified into two main categories based on their origin:

1. Nuclear-encoded mitochondrial proteins (NEMPs): These are proteins that are encoded by genes located in the nucleus, synthesized in the cytoplasm, and then imported into the mitochondria through specific import pathways. NEMPs make up about 99% of all mitochondrial proteins and are involved in various functions such as oxidative phosphorylation, tricarboxylic acid (TCA) cycle, fatty acid oxidation, and mitochondrial dynamics.

2. Mitochondrial DNA-encoded proteins (MEPs): These are proteins that are encoded by the mitochondrial genome, synthesized within the mitochondria, and play essential roles in the electron transport chain (ETC), a key component of oxidative phosphorylation. The human mitochondrial genome encodes only 13 proteins, all of which are subunits of complexes I, III, IV, and V of the ETC.

Defects in mitochondrial proteins can lead to various mitochondrial disorders, which often manifest as neurological, muscular, or metabolic symptoms due to impaired energy production. These disorders are usually caused by mutations in either nuclear or mitochondrial genes that encode mitochondrial proteins.

Cytochrome c is a small protein that is involved in the electron transport chain, a key part of cellular respiration in which cells generate energy in the form of ATP. Cytochrome c contains a heme group, which binds to and transports electrons. The cytochrome c group refers to a class of related cytochromes that have similar structures and functions. These proteins are found in the mitochondria of eukaryotic cells (such as those of plants and animals) and in the inner membranes of bacteria. They play a crucial role in the production of energy within the cell, and are also involved in certain types of programmed cell death (apoptosis).

Mitochondria are specialized structures located inside cells that convert the energy from food into ATP (adenosine triphosphate), which is the primary form of energy used by cells. They are often referred to as the "powerhouses" of the cell because they generate most of the cell's supply of chemical energy. Mitochondria are also involved in various other cellular processes, such as signaling, differentiation, and apoptosis (programmed cell death).

Mitochondria have their own DNA, known as mitochondrial DNA (mtDNA), which is inherited maternally. This means that mtDNA is passed down from the mother to her offspring through the egg cells. Mitochondrial dysfunction has been linked to a variety of diseases and conditions, including neurodegenerative disorders, diabetes, and aging.

Sulfite oxidase is a medical term that refers to an enzyme found in the human body, primarily in the liver and brain. This enzyme plays a crucial role in the metabolism of sulfur-containing amino acids, such as methionine and cysteine.

Sulfite oxidase catalyzes the conversion of sulfites to sulfates, which is an essential step in the detoxification of sulfur-containing compounds. The enzyme requires molybdenum and heme cofactors for its activity. A deficiency in this enzyme can lead to a rare genetic disorder known as sulfite oxidase deficiency, which is characterized by developmental delay, seizures, and severe neurological symptoms.

Metabolic brain diseases are a group of disorders caused by genetic defects that affect the body's metabolism and result in abnormal accumulation of harmful substances in the brain. These conditions are present at birth (inborn) or develop during infancy or early childhood. Examples of metabolic brain diseases that are present at birth include:

1. Phenylketonuria (PKU): A disorder caused by a deficiency of the enzyme phenylalanine hydroxylase, which leads to an accumulation of phenylalanine in the brain and can cause intellectual disability, seizures, and behavioral problems if left untreated.
2. Maple syrup urine disease (MSUD): A disorder caused by a deficiency of the enzyme branched-chain ketoacid dehydrogenase, which leads to an accumulation of branched-chain amino acids in the body and can cause intellectual disability, seizures, and metabolic crisis if left untreated.
3. Urea cycle disorders: A group of disorders caused by defects in enzymes that help remove ammonia from the body. Accumulation of ammonia in the blood can lead to brain damage, coma, or death if not treated promptly.
4. Organic acidemias: A group of disorders caused by defects in enzymes that help break down certain amino acids and other organic compounds. These conditions can cause metabolic acidosis, seizures, and developmental delays if left untreated.

Early diagnosis and treatment of these conditions are crucial to prevent irreversible brain damage and other complications. Treatment typically involves dietary restrictions, supplements, and medications to manage the underlying metabolic imbalance. In some cases, enzyme replacement therapy or liver transplantation may be necessary.

Cytochromes c are a group of small heme proteins found in the mitochondria of cells, involved in the electron transport chain and play a crucial role in cellular respiration. They accept and donate electrons during the process of oxidative phosphorylation, which generates ATP, the main energy currency of the cell. Cytochromes c contain a heme group, an organic compound that includes iron, which facilitates the transfer of electrons. The "c" in cytochromes c refers to the type of heme group they contain (cyt c has heme c). They are highly conserved across species and have been widely used as a molecular marker for evolutionary studies.

A mutation is a permanent change in the DNA sequence of an organism's genome. Mutations can occur spontaneously or be caused by environmental factors such as exposure to radiation, chemicals, or viruses. They may have various effects on the organism, ranging from benign to harmful, depending on where they occur and whether they alter the function of essential proteins. In some cases, mutations can increase an individual's susceptibility to certain diseases or disorders, while in others, they may confer a survival advantage. Mutations are the driving force behind evolution, as they introduce new genetic variability into populations, which can then be acted upon by natural selection.

Cytochromes are a type of hemeprotein found in the mitochondria and other cellular membranes of organisms. They contain a heme group, which is a prosthetic group composed of an iron atom surrounded by a porphyrin ring. This structure allows cytochromes to participate in redox reactions, acting as electron carriers in various biological processes.

There are several types of cytochromes, classified based on the type of heme they contain and their absorption spectra. Some of the most well-known cytochromes include:

* Cytochrome c: a small, mobile protein found in the inner mitochondrial membrane that plays a crucial role in the electron transport chain during cellular respiration.
* Cytochrome P450: a large family of enzymes involved in the metabolism of drugs, toxins, and other xenobiotics. They are found in various tissues, including the liver, lungs, and skin.
* Cytochrome b: a component of several electron transport chains, including those found in mitochondria, bacteria, and chloroplasts.

Cytochromes play essential roles in energy production, detoxification, and other metabolic processes, making them vital for the survival and function of living organisms.

Inborn errors of amino acid metabolism refer to genetic disorders that affect the body's ability to properly break down and process individual amino acids, which are the building blocks of proteins. These disorders can result in an accumulation of toxic levels of certain amino acids or their byproducts in the body, leading to a variety of symptoms and health complications.

There are many different types of inborn errors of amino acid metabolism, each affecting a specific amino acid or group of amino acids. Some examples include:

* Phenylketonuria (PKU): This disorder affects the breakdown of the amino acid phenylalanine, leading to its accumulation in the body and causing brain damage if left untreated.
* Maple syrup urine disease: This disorder affects the breakdown of the branched-chain amino acids leucine, isoleucine, and valine, leading to their accumulation in the body and causing neurological problems.
* Homocystinuria: This disorder affects the breakdown of the amino acid methionine, leading to its accumulation in the body and causing a range of symptoms including developmental delay, intellectual disability, and cardiovascular problems.

Treatment for inborn errors of amino acid metabolism typically involves dietary restrictions or supplementation to manage the levels of affected amino acids in the body. In some cases, medication or other therapies may also be necessary. Early diagnosis and treatment can help prevent or minimize the severity of symptoms and health complications associated with these disorders.

The Cytochrome P-450 (CYP450) enzyme system is a group of enzymes found primarily in the liver, but also in other organs such as the intestines, lungs, and skin. These enzymes play a crucial role in the metabolism and biotransformation of various substances, including drugs, environmental toxins, and endogenous compounds like hormones and fatty acids.

The name "Cytochrome P-450" refers to the unique property of these enzymes to bind to carbon monoxide (CO) and form a complex that absorbs light at a wavelength of 450 nm, which can be detected spectrophotometrically.

The CYP450 enzyme system is involved in Phase I metabolism of xenobiotics, where it catalyzes oxidation reactions such as hydroxylation, dealkylation, and epoxidation. These reactions introduce functional groups into the substrate molecule, which can then undergo further modifications by other enzymes during Phase II metabolism.

There are several families and subfamilies of CYP450 enzymes, each with distinct substrate specificities and functions. Some of the most important CYP450 enzymes include:

1. CYP3A4: This is the most abundant CYP450 enzyme in the human liver and is involved in the metabolism of approximately 50% of all drugs. It also metabolizes various endogenous compounds like steroids, bile acids, and vitamin D.
2. CYP2D6: This enzyme is responsible for the metabolism of many psychotropic drugs, including antidepressants, antipsychotics, and beta-blockers. It also metabolizes some endogenous compounds like dopamine and serotonin.
3. CYP2C9: This enzyme plays a significant role in the metabolism of warfarin, phenytoin, and nonsteroidal anti-inflammatory drugs (NSAIDs).
4. CYP2C19: This enzyme is involved in the metabolism of proton pump inhibitors, antidepressants, and clopidogrel.
5. CYP2E1: This enzyme metabolizes various xenobiotics like alcohol, acetaminophen, and carbon tetrachloride, as well as some endogenous compounds like fatty acids and prostaglandins.

Genetic polymorphisms in CYP450 enzymes can significantly affect drug metabolism and response, leading to interindividual variability in drug efficacy and toxicity. Understanding the role of CYP450 enzymes in drug metabolism is crucial for optimizing pharmacotherapy and minimizing adverse effects.

Cytochrome c1 is a protein that is a part of the electron transport chain in the inner mitochondrial membrane. It is a component of Complex III, also known as the cytochrome bc1 complex. Cytochrome c1 contains a heme group and plays a role in the transfer of electrons from ubiquinol to cytochrome c during oxidative phosphorylation, which is the process by which cells generate energy in the form of ATP. Defects in cytochrome c1 can lead to mitochondrial disorders and have been implicated in the development of certain diseases, such as neurodegenerative disorders and cancer.

The Electron Transport Chain (ETC) is a series of complexes in the inner mitochondrial membrane that are involved in the process of cellular respiration. It is the final pathway for electrons derived from the oxidation of nutrients such as glucose, fatty acids, and amino acids to be transferred to molecular oxygen. This transfer of electrons drives the generation of a proton gradient across the inner mitochondrial membrane, which is then used by ATP synthase to produce ATP, the main energy currency of the cell.

The electron transport chain consists of four complexes (I-IV) and two mobile electron carriers (ubiquinone and cytochrome c). Electrons from NADH and FADH2 are transferred to Complex I and Complex II respectively, which then pass them along to ubiquinone. Ubiquinone then transfers the electrons to Complex III, which passes them on to cytochrome c. Finally, cytochrome c transfers the electrons to Complex IV, where they combine with oxygen and protons to form water.

The transfer of electrons through the ETC is accompanied by the pumping of protons from the mitochondrial matrix to the intermembrane space, creating a proton gradient. The flow of protons back across the inner membrane through ATP synthase drives the synthesis of ATP from ADP and inorganic phosphate.

Overall, the electron transport chain is a crucial process for generating energy in the form of ATP in the cell, and it plays a key role in many metabolic pathways.

Oxidation-Reduction (redox) reactions are a type of chemical reaction involving a transfer of electrons between two species. The substance that loses electrons in the reaction is oxidized, and the substance that gains electrons is reduced. Oxidation and reduction always occur together in a redox reaction, hence the term "oxidation-reduction."

In biological systems, redox reactions play a crucial role in many cellular processes, including energy production, metabolism, and signaling. The transfer of electrons in these reactions is often facilitated by specialized molecules called electron carriers, such as nicotinamide adenine dinucleotide (NAD+/NADH) and flavin adenine dinucleotide (FAD/FADH2).

The oxidation state of an element in a compound is a measure of the number of electrons that have been gained or lost relative to its neutral state. In redox reactions, the oxidation state of one or more elements changes as they gain or lose electrons. The substance that is oxidized has a higher oxidation state, while the substance that is reduced has a lower oxidation state.

Overall, oxidation-reduction reactions are fundamental to the functioning of living organisms and are involved in many important biological processes.

Cytochrome a is a type of cytochrome found in the inner mitochondrial membrane of eukaryotic cells. It is a component of cytochrome c oxidase, the final enzyme in the electron transport chain responsible for reducing molecular oxygen to water during cellular respiration. Cytochrome a contains a heme group with a low redox potential, making it capable of accepting electrons from cytochrome c and transferring them to oxygen.

The "Cytochrome a Group" typically refers to a family of related cytochromes that share similar structural and functional properties, including the presence of a heme group with a low redox potential. This group includes cytochrome a, as well as other closely related cytochromes such as cytochrome aa3 and cytochrome o. These cytochromes play important roles in electron transfer and energy conservation during cellular respiration in various organisms.

"Paracoccus denitrificans" is not a medical term, but rather a term used in the field of microbiology. It refers to a species of gram-negative, facultatively anaerobic bacteria that are commonly found in soil and water environments. These bacteria are known for their ability to carry out denitrification, which is the process of converting nitrate (NO3-) to nitrogen gas (N2) under anaerobic conditions. This ability makes them important players in the global nitrogen cycle.

While "Paracoccus denitrificans" itself is not a medical term, certain strains of this bacterium have been used in medical research and biotechnology applications. For example, some researchers have studied the use of "Paracoccus denitrificans" as a potential agent for removing nitrogenous compounds from wastewater or for producing hydrogen gas through fermentation. However, there is no direct medical relevance to this bacterium in terms of human health or disease.

Oxidoreductases are a class of enzymes that catalyze oxidation-reduction reactions, which involve the transfer of electrons from one molecule (the reductant) to another (the oxidant). These enzymes play a crucial role in various biological processes, including energy production, metabolism, and detoxification.

The oxidoreductase-catalyzed reaction typically involves the donation of electrons from a reducing agent (donor) to an oxidizing agent (acceptor), often through the transfer of hydrogen atoms or hydride ions. The enzyme itself does not undergo any permanent chemical change during this process, but rather acts as a catalyst to lower the activation energy required for the reaction to occur.

Oxidoreductases are classified and named based on the type of electron donor or acceptor involved in the reaction. For example, oxidoreductases that act on the CH-OH group of donors are called dehydrogenases, while those that act on the aldehyde or ketone groups are called oxidases. Other examples include reductases, peroxidases, and catalases.

Understanding the function and regulation of oxidoreductases is important for understanding various physiological processes and developing therapeutic strategies for diseases associated with impaired redox homeostasis, such as cancer, neurodegenerative disorders, and cardiovascular disease.

Cytochrome b is a type of cytochrome, which is a class of proteins that contain heme as a cofactor and are involved in electron transfer. Cytochromes are classified based on the type of heme they contain and their absorption spectra.

The cytochrome b group includes several subfamilies of cytochromes, including cytochrome b5, cytochrome b2, and cytochrome bc1 (also known as complex III). These cytochromes are involved in various biological processes, such as fatty acid desaturation, steroid metabolism, and the electron transport chain.

The electron transport chain is a series of protein complexes in the inner mitochondrial membrane that generates most of the ATP (adenosine triphosphate) required for cellular energy production. Cytochrome bc1 is a key component of the electron transport chain, where it functions as a dimer and catalyzes the transfer of electrons from ubiquinol to cytochrome c while simultaneously pumping protons across the membrane. This creates an electrochemical gradient that drives ATP synthesis.

Deficiencies or mutations in cytochrome b genes can lead to various diseases, such as mitochondrial disorders and cancer.

Heme is not a medical term per se, but it is a term used in the field of medicine and biology. Heme is a prosthetic group found in hemoproteins, which are proteins that contain a heme iron complex. This complex plays a crucial role in various biological processes, including oxygen transport (in hemoglobin), electron transfer (in cytochromes), and chemical catalysis (in peroxidases and catalases).

The heme group consists of an organic component called a porphyrin ring, which binds to a central iron atom. The iron atom can bind or release electrons, making it essential for redox reactions in the body. Heme is also vital for the formation of hemoglobin and myoglobin, proteins responsible for oxygen transport and storage in the blood and muscles, respectively.

In summary, heme is a complex organic-inorganic structure that plays a critical role in several biological processes, particularly in electron transfer and oxygen transport.

Mitochondria in muscle, also known as the "powerhouses" of the cell, are organelles that play a crucial role in generating energy for muscle cells through a process called cellular respiration. They convert the chemical energy found in glucose and oxygen into ATP (adenosine triphosphate), which is the main source of energy used by cells.

Muscle cells contain a high number of mitochondria due to their high energy demands for muscle contraction and relaxation. The number and size of mitochondria in muscle fibers can vary depending on the type of muscle fiber, with slow-twitch, aerobic fibers having more numerous and larger mitochondria than fast-twitch, anaerobic fibers.

Mitochondrial dysfunction has been linked to various muscle disorders, including mitochondrial myopathies, which are characterized by muscle weakness, exercise intolerance, and other symptoms related to impaired energy production in the muscle cells.

A proton pump is a specialized protein structure that functions as an enzyme, known as a proton pump ATPase, which actively transports hydrogen ions (protons) across a membrane. This process creates a gradient of hydrogen ions, resulting in an electrochemical potential difference, also known as a proton motive force. The main function of proton pumps is to generate and maintain this gradient, which can be used for various purposes, such as driving the synthesis of ATP (adenosine triphosphate) or transporting other molecules against their concentration gradients.

In the context of gastric physiology, the term "proton pump" often refers to the H+/K+-ATPase present in the parietal cells of the stomach. This proton pump is responsible for secreting hydrochloric acid into the stomach lumen, contributing to the digestion and sterilization of ingested food. Inhibiting this specific proton pump with medications like proton pump inhibitors (PPIs) is a common treatment strategy for gastric acid-related disorders such as gastroesophageal reflux disease (GERD), peptic ulcers, and Zollinger-Ellison syndrome.

Cytochrome c2 is a type of cytochrome, which is a small water-soluble protein involved in electron transport chains and associated with the inner membrane of mitochondria. Cytochrome c2 specifically contains heme as a cofactor and plays a role in the respiratory chain of certain bacteria, contributing to their energy production through oxidative phosphorylation. It is not found in human or mammalian cells.

Spectrophotometry is a technical analytical method used in the field of medicine and science to measure the amount of light absorbed or transmitted by a substance at specific wavelengths. This technique involves the use of a spectrophotometer, an instrument that measures the intensity of light as it passes through a sample.

In medical applications, spectrophotometry is often used in laboratory settings to analyze various biological samples such as blood, urine, and tissues. For example, it can be used to measure the concentration of specific chemicals or compounds in a sample by measuring the amount of light that is absorbed or transmitted at specific wavelengths.

In addition, spectrophotometry can also be used to assess the properties of biological tissues, such as their optical density and thickness. This information can be useful in the diagnosis and treatment of various medical conditions, including skin disorders, eye diseases, and cancer.

Overall, spectrophotometry is a valuable tool for medical professionals and researchers seeking to understand the composition and properties of various biological samples and tissues.

Porphyrins are complex organic compounds that contain four pyrrole rings joined together by methine bridges (=CH-). They play a crucial role in the biochemistry of many organisms, as they form the core structure of various heme proteins and other metalloproteins. Some examples of these proteins include hemoglobin, myoglobin, cytochromes, and catalases, which are involved in essential processes such as oxygen transport, electron transfer, and oxidative metabolism.

In the human body, porphyrins are synthesized through a series of enzymatic reactions known as the heme biosynthesis pathway. Disruptions in this pathway can lead to an accumulation of porphyrins or their precursors, resulting in various medical conditions called porphyrias. These disorders can manifest as neurological symptoms, skin lesions, and gastrointestinal issues, depending on the specific type of porphyria and the site of enzyme deficiency.

It is important to note that while porphyrins are essential for life, their accumulation in excessive amounts or at inappropriate locations can result in pathological conditions. Therefore, understanding the regulation and function of porphyrin metabolism is crucial for diagnosing and managing porphyrias and other related disorders.

In the context of medicine, iron is an essential micromineral and key component of various proteins and enzymes. It plays a crucial role in oxygen transport, DNA synthesis, and energy production within the body. Iron exists in two main forms: heme and non-heme. Heme iron is derived from hemoglobin and myoglobin in animal products, while non-heme iron comes from plant sources and supplements.

The recommended daily allowance (RDA) for iron varies depending on age, sex, and life stage:

* For men aged 19-50 years, the RDA is 8 mg/day
* For women aged 19-50 years, the RDA is 18 mg/day
* During pregnancy, the RDA increases to 27 mg/day
* During lactation, the RDA for breastfeeding mothers is 9 mg/day

Iron deficiency can lead to anemia, characterized by fatigue, weakness, and shortness of breath. Excessive iron intake may result in iron overload, causing damage to organs such as the liver and heart. Balanced iron levels are essential for maintaining optimal health.

Heme proteins are a type of protein that contain a heme group, which is a prosthetic group composed of an iron atom contained in the center of a large organic ring called a porphyrin. The heme group gives these proteins their characteristic red color. Hemeproteins have various important functions in biological systems, including oxygen transport (e.g., hemoglobin), electron transfer (e.g., cytochromes), and enzymatic catalysis (e.g., peroxidases and catalases). The heme group can bind and release gases, such as oxygen and carbon monoxide, and can participate in redox reactions due to the ease with which iron can change its oxidation state.