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Bioinorganic compounds

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The most commonly known and studied "bioinorganic" compounds of iron (i.e., iron compounds used in biology) are the heme proteins: examples are hemoglobin, myoglobin, and cytochrome P450.

These compounds can transport gases, build enzymes, and be used in transferring electrons.

Metalloproteins are a group of proteins with metal ion cofactors. Some examples of iron metalloproteins are ferritin and rubredoxin. Many enzymes vital to life contain iron, such as catalase, lipoxygenases, and IRE-BP. Iron-responsive element-binding protein. The iron-responsive element-binding proteins, also known as IRE-BP, IRBP, IRP and IFR ,[1] bind to iron-responsive elements (IREs) in the regulation of human iron metabolism.[2] Function[edit] ACO1, or IRP1, is a bifunctional protein that functions as an iron-responsive element (IRE)-binding protein involved in the control of iron metabolism by binding mRNA to repress translation or degradation.

Iron-responsive element-binding protein

It functions also as the cytoplasmic isoform of aconitase. Aconitases are iron-sulfur proteins that require a 4Fe-4S cluster for their enzymatic activity, in which they catalyze conversion of citrate to isocitrate.[2] This structure was based on x-ray crystal diffraction. The resolution was 2.80 Å. Iron transport[edit] All cells use some iron, and must get it from the circulating blood. Transferrin receptor production depends on a similar mechanism. In low-iron conditions, IRE-BPs allow the cell to keep producing transferrin receptors. Lipoxygenase. Lipoxygenases (EC 1.13.11.-) are a family of iron-containing enzymes that catalyze the dioxygenation of polyunsaturated fatty acids in lipids containing a cis,cis-1,4- pentadiene structure.

Lipoxygenase

It catalyses the following reaction: Fatty acid + O2 = fatty acid hydroperoxide Lipoxygenases are found in plants, animals and fungi. Catalase. Catalase is a common enzyme found in nearly all living organisms exposed to oxygen (such as bacteria, plants, and animals).

Catalase

It catalyzes the decomposition of hydrogen peroxide to water and oxygen.[1] It is a very important enzyme in protecting the cell from oxidative damage by reactive oxygen species (ROS). Likewise, catalase has one of the highest turnover numbers of all enzymes; one catalase molecule can convert approximately 5 million molecules[2] of hydrogen peroxide to water and oxygen each second.[3] Catalase is a tetramer of four polypeptide chains, each over 500 amino acids long.[4] It contains four porphyrin heme (iron) groups that allow the enzyme to react with the hydrogen peroxide. History[edit] Catalase was not noticed until 1818 when Louis Jacques Thénard, who discovered H2O2 (hydrogen peroxide), suggested its breakdown is caused by an unknown substance. Rubredoxin. Rubredoxins are a class of low-molecular-weight iron-containing proteins found in sulfur-metabolizing bacteria and archaea.

Rubredoxin

Sometimes rubredoxins are classified as iron-sulfur proteins; however, in contrast to iron-sulfur proteins, rubredoxins do not contain inorganic sulfide. Like cytochromes, ferredoxins and Rieske proteins, rubredoxins participate in electron transfer in biological systems. Ferritin. Ferritin is a ubiquitous intracellular protein that stores iron and releases it in a controlled fashion.

Ferritin

The protein is produced by almost all living organisms, including algae, bacteria, higher plants, and animals. Metalloprotein. Function[edit] Coordination chemistry principles[edit] In metalloproteins, metal ions are usually coordinated by nitrogen, oxygen or sulfur centres belonging to amino acid residues of the protein.

Metalloprotein

These donor groups are often provided by side-chains on the amino acid residues. Especially important are the imidazole substituent in histidine residues, thiolate substituents in cysteinyl residues, and carboxylate groups provided by aspartate. Given the diversity of the metalloproteome, virtually all amino acid residues have been shown to bind metal centers. In addition to donor groups that are provided by amino acid residues, a large number of organic cofactors function as ligands. Cytochrome P450. The cytochrome P450 superfamily of monooxygenases (officially abbreviated as CYP) is a large and diverse group of enzymes that catalyze the oxidation of organic substances.

Cytochrome P450

The substrates of CYP enzymes include metabolic intermediates such as lipids and steroidal hormones, as well as xenobiotic substances such as drugs and other toxic chemicals. CYPs are the major enzymes involved in drug metabolism and bioactivation, accounting for about 75% of the total number of different metabolic reactions.[1] The most common reaction catalyzed by cytochromes P450 is a monooxygenase reaction, e.g., insertion of one atom of oxygen into the aliphatic position of an organic substrate (RH) while the other oxygen atom is reduced to water: Most CYPs require a protein partner to deliver one or more electrons to reduce the iron (and eventually molecular oxygen). Myoglobin. Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals.

Myoglobin

It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. In humans, myoglobin is only found in the bloodstream after muscle injury. It is an abnormal finding, and can be diagnostically relevant when found in blood. [2] Myoglobin is the primary oxygen-carrying pigment of muscle tissues.[3] High concentrations of myoglobin in muscle cells allow organisms to hold their breath for a longer period of time. Diving mammals such as whales and seals have muscles with particularly high abundance of myoglobin.[2] Myoglobin is found in Type I muscle, Type II A and Type II B, but most texts consider myoglobin not to be found in smooth muscle. Hemoglobin. Hemoglobin (/ˈhiːmɵˌɡloʊbɨn/); also spelled haemoglobin and abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates[1] (with the exception of the fish family Channichthyidae[2]) as well as the tissues of some invertebrates.

Hemoglobin

Hemoglobin in the blood carries oxygen from the respiratory organs (lungs or gills) to the rest of the body (i.e. the tissues). There it releases the oxygen to permit aerobic respiration to provide energy to power the functions of the organism in the process called metabolism. Heme. Ball and Stick model of Heme B Function[edit] Hemoproteins have diverse biological functions including the transportation of diatomic gases, chemical catalysis, diatomic gas detection, and electron transfer.

Heme

The heme ion serves as a source or sink of electrons during electron transfer or redox chemistry. In peroxidase reactions, the porphyrin molecule also serves as an electron source. In the transportation or detection of diatomic gases, the gas binds to the heme ion.