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Cystathionine
Cystathionine is an intermediate in the synthesis of cysteine. Cystathionine is produced by the transsulfuration pathway which converts homocysteine into cystathionine. Cystathionine is then used by the enzymes cystathionine gamma-lyase (CTH), cysteine dioxygenase (CDO), and sulfinoalanine decarboxylase to produce hypotaurine and then taurine. Alternately, the cysteine from the cystathionine gamma-lyase can be used by the enzymes glutamate–cysteine ligase (GCL) and glutathione synthetase (GSS) to produce glutathione. An excess of cystathionine in the urine is called cystathioninuria. Biosynthetically, cystathionine is generated from homocysteine and serine by cystathionine beta synthase (upper reaction in the diagram below). It is then cleaved into cysteine and α-ketobutyrate by cystathionine gamma-lyase (lower reaction). References {{Amino acid metabolism intermediates Sulfur amino acids ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cystathionine Beta Synthase
Cystathionine-β-synthase, also known as CBS, is an enzyme () that in humans is encoded by the ''CBS'' gene. It catalyzes the first step of the transsulfuration pathway, from homocysteine to cystathionine: :Serine, L-serine + homocysteine, L-homocysteine \rightleftharpoons cystathionine, L-cystathionine + water (molecule), H2O CBS uses the Cofactor (biochemistry), cofactor pyridoxal-phosphate (PLP) and can be allosterically regulated by effectors such as the ubiquitous cofactor S-adenosyl-L-methionine (adoMet). This enzyme belongs to the family of lyases, to be specific, the hydro-lyases, which cleave carbon-oxygen bonds. CBS is a multidomain enzyme composed of an N-terminal enzymatic domain and two CBS domains. The ''CBS'' gene is the most common locus for mutations associated with homocystinuria. Nomenclature The List of enzymes, systematic name of this enzyme class is L-serine hydro-lyase (adding homocysteine; L-cystathionine-forming). Other names in common use include: * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transsulfuration Pathway
The transsulfuration pathway is a metabolic pathway involving the interconversion of cysteine and homocysteine through the intermediate cystathionine. Two transsulfurylation pathways are known: the ''forward'' and the ''reverse''. The ''forward pathway'' is present in several bacteria, such as ''Escherichia coli'' and ''Bacillus subtilis'', and involves the transfer of the thiol group from cysteine to homocysteine (methionine precursor with the S-methyl group), thanks to the γ-replacement of the acetyl or succinyl group of a homoserine with cysteine via its thiol group to form cystathionine (catalysed by cystathionine γ-synthase, which is encoded by ''metB'' in ''E. coli'' and ''metI'' in ''B. subtilis''). Cystathionine is then cleaved by means of the β-elimination of the homocysteine portion of the molecule leaving behind an unstable imino acid, which is attacked by water to form pyruvate and ammonia (catalysed by the metC-encoded cystathionine β-lyase). The production of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homocysteine
Homocysteine is a non-proteinogenic α-amino acid. It is a homologue of the amino acid cysteine, differing by an additional methylene bridge (-CH2-). It is biosynthesized from methionine by the removal of its terminal Cε methyl group. In the body, homocysteine can be recycled into methionine or converted into cysteine with the aid of certain B-vitamins. High levels of homocysteine in the blood (hyperhomocysteinemia) is regarded as a marker of cardiovascular disease, likely working through atherogenesis, which can result in ischemic injury. Therefore, hyperhomocysteinemia is a possible risk factor for coronary artery disease. Coronary artery disease occurs when an atherosclerotic plaque blocks blood flow to the coronary arteries, which supply the heart with oxygenated blood. Hyperhomocysteinemia has been correlated with the occurrence of blood clots, heart attacks, and strokes, although it is unclear whether hyperhomocysteinemia is an independent risk factor for these conditi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cystathionine Gamma-lyase
The enzyme cystathionine γ-lyase (EC 4.4.1.1, CTH or CSE; also cystathionase; systematic name L-cystathionine cysteine-lyase (deaminating; 2-oxobutanoate-forming)) breaks down cystathionine into cysteine, 2-oxobutanoate ( α-ketobutyrate), and ammonia: :L-cystathionine + H2O = L-cysteine + 2-oxobutanoate + NH3 (overall reaction) ::(1a) L-cystathionine = L-cysteine + 2-aminobut-2-enoate ::(1b) 2-aminobut-2-enoate = 2-iminobutanoate (spontaneous) ::(1c) 2-iminobutanoate + H2O = 2-oxobutanoate + NH3 (spontaneous) Pyridoxal phosphate is a prosthetic group of this enzyme. Cystathionine γ-lyase also catalyses the following elimination reactions: * L-homoserine to form H2O, NH3 and 2-oxobutanoate * L-cystine, producing thiocysteine, pyruvate and NH3 * L-cysteine producing pyruvate, NH3 and H2S In some bacteria and mammals, including humans, this enzyme takes part in generating hydrogen sulfide. Hydrogen sulfide is one of a few gases that was recently discovered to have a role in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cystathioninuria
Cystathioninuria, also called cystathionase deficiency, is an autosomal recessive metabolic disorder. It is characterized by an abnormal accumulation of plasma cystathionine leading to excess cystathionine in the urine. Hereditary cystathioninuria is associated with the reduced activity of the enzyme cystathionine gamma-lyase. It is considered a biochemical anomaly. This is because it associated with a wide range of diseases and its inconsistency. Cystathionase catalyzes cystathionine to cysteine and α-ketobutyrate. Cysteine is an essential amino acid and its conversion from cystathionine occurs in the trans-sulfuration pathway. The availability of cysteine is necessary for the synthesis of an important anti-oxidant, glutathione. Cystathionase has a co-enzyme, pyridoxal phosphate, which is the active form the vitamin B6. This means that vitamin B6 is essential for the function of cystathionase. Cystathioninuria can be broken down into two main categories. Primary cystathioninuri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cysteine
Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometimes the symbol Cyz is used. The deprotonated form can generally be described by the symbol Cym as well. The thiol is susceptible to oxidation to give the disulfide derivative cystine, which serves an important structural role in many proteins. In this case, the symbol Cyx is sometimes used. When used as a food additive, it has the E number E920. Cysteine is encoded by the codons UGU and UGC. The sulfur-containing amino acids cysteine and methionine are more easily oxidized than the other amino acids. Structure Like other amino acids (not as a residue of a protein), cysteine exists as a zwitterion. Cysteine has chirality in the older / notation based on homology to - and -glyceraldehyde. In the newer ''R''/''S'' system of designating chi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cysteine Biosynthesis Unlabeled
Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the formula . The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. When present as a deprotonated catalytic residue, sometimes the symbol Cyz is used. The deprotonated form can generally be described by the symbol Cym as well. The thiol is susceptible to oxidation to give the disulfide derivative cystine, which serves an important structural role in many proteins. In this case, the symbol Cyx is sometimes used. When used as a food additive, it has the E number E920. Cysteine is encoded by the codons UGU and UGC. The sulfur-containing amino acids cysteine and methionine are more easily oxidized than the other amino acids. Structure Like other amino acids (not as a residue of a protein), cysteine exists as a zwitterion. Cysteine has chirality in the older / notation based on homology to - and -glyceraldehyde. In the newer ''R''/''S'' system of designating chir ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Serine
Serine (symbol Ser or S) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated − form under biological conditions), a carboxyl group (which is in the deprotonated − form under biological conditions), and a side chain consisting of a hydroxymethyl group, classifying it as a polar amino acid. It can be synthesized in the human body under normal physiological circumstances, making it a nonessential amino acid. It is encoded by the codons UCU, UCC, UCA, UCG, AGU and AGC. Occurrence This compound is one of the naturally occurring proteinogenic amino acids. Only the L-stereoisomer appears naturally in proteins. It is not essential to the human diet, since it is synthesized in the body from other metabolites, including glycine. Serine was first obtained from silk protein, a particularly rich source, in 1865 by Emil Cramer. Its name is derived from the Latin for silk, ''sericum''. Serine's structure was estab ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cysteine Dioxygenase
Cysteine dioxygenase (CDO) is a non-heme iron enzyme that catalyzes the conversion of L-cysteine to cysteine sulfinic acid (cysteine sulfinate). CDO plays an important role in cysteine catabolism, regulating intracellular levels of cysteine and responding changes in cysteine availability. As such, CDO is highly regulated and undergoes large changes in concentration and efficiency. It oxidizes cysteine to the corresponding sulfinic acid by activation of dioxygen, although the exact mechanism of the reaction is still unclear. In addition to being found in mammals, CDO also exists in some yeast and bacteria, although the exact function is still unknown. CDO has been implicated in various Neurodegeneration, neurodegenerative diseases and cancers, which is likely related to cysteine toxicity. Function CDO is responsible for the first major step in metabolism of cysteine. CDO oxidizes to cysteine sulfinic acid (which exists predominantly in the anionic sulfinate form ''in vivo''). Overa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sulfinoalanine Decarboxylase
The enzyme sulfinoalanine decarboxylase () catalyzes the chemical reaction :3-sulfino-L-alanine \rightleftharpoons hypotaurine + CO2 Hence, this enzyme has one substrate, 3-sulfino-L-alanine (also known as Cysteine sulfinic acid), and two products, hypotaurine and CO2. This enzyme belongs to the family of lyases, specifically the carboxy-lyases, which cleave carbon-carbon bonds. The systematic name of this enzyme class is 3-sulfino-L-alanine carboxy-lyase (hypotaurine-forming). Other names in common use include cysteine-sulfinate decarboxylase, L-cysteinesulfinic acid decarboxylase, cysteine-sulfinate decarboxylase, CADCase/CSADCase, CSAD, cysteic decarboxylase, cysteinesulfinic acid decarboxylase, cysteinesulfinate decarboxylase, sulfoalanine decarboxylase, and 3-sulfino-L-alanine carboxy-lyase. This enzyme participates in taurine metabolism. It employs one cofactor, pyridoxal phosphate. Structural studies As of late 2007, only one structure A structure is an arrangem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypotaurine
Hypotaurine is a sulfinic acid that is an intermediate in the biosynthesis of taurine. Like taurine, it also acts as an endogenous neurotransmitter via action on the glycine receptors. It is an osmolyte with antioxidant properties. Hypotaurine is derived from cysteine (and homocysteine). In mammals, the biosynthesis of hypotaurine from cysteine occurs in the pancreas. In the cysteine sulfinic acid pathway, cysteine is first oxidized to its sulfinic acid, catalyzed by the enzyme cysteine dioxygenase Cysteine dioxygenase (CDO) is a non-heme iron enzyme that catalyzes the conversion of L-cysteine to cysteine sulfinic acid (cysteine sulfinate). CDO plays an important role in cysteine catabolism, regulating intracellular levels of cysteine and res .... Cysteine sulfinic acid, in turn, is decarboxylated by sulfinoalanine decarboxylase to form hypotaurine. Hypotaurine is enzymatically oxidized to yield taurine by hypotaurine dehydrogenase. References Amines Sulfinic acids ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Taurine
Taurine (), or 2-aminoethanesulfonic acid, is an organic compound that is widely distributed in animal tissues. It is a major constituent of bile and can be found in the large intestine, and accounts for up to 0.1% of total human body weight. It is named after Latin (cognate to Ancient Greek ταῦρος, ''taûros'') meaning bull or ox, as it was first isolated from ox bile in 1827 by German scientists Friedrich Tiedemann and Leopold Gmelin. It was discovered in human bile in 1846 by Edmund Ronalds. It has many biological roles, such as conjugation of bile acids, antioxidation, osmoregulation, membrane stabilization, and modulation of calcium signaling. It is essential for cardiovascular function, and development and function of skeletal muscle, the retina, and the central nervous system. It is an unusual example of a naturally occurring sulfonic acid. Chemical and biochemical features Taurine exists as a zwitterion , as verified by X-ray crystallography. The sulfonic aci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
