Selenocysteine is the 21st proteinogenic amino acid. Selenoproteins contain selenocysteine residues. Selenocysteine is an analogue of the more common cysteine with selenium in place of the sulfur.
Cysteine is a semiessential proteinogenic amino acid with the formula HOOC−CH(−NH2)−CH2−SH. The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. Cysteine is chiral, only L-cysteine is found in nature.
Methionine is an essential amino acid in humans.
Taurine, or 2-aminoethanesulfonic acid, is a non-proteinogenic amino sulfonic acid 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.
Cysteine dioxygenase (CDO) is a non-heme iron enzyme that catalyzes the conversion of L-cysteine to cysteine sulfinic acid. 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 neurodegenerative diseases and cancers, which is likely related to cysteine toxicity.
Nitrilase enzymes catalyse the hydrolysis of nitriles to carboxylic acids and ammonia, without the formation of "free" amide intermediates. Nitrilases are involved in natural product biosynthesis and post translational modifications in plants, animals, fungi and certain prokaryotes. Nitrilases can also be used as catalysts in preparative organic chemistry. Among others, nitrilases have been used for the resolution of racemic mixtures. Nitrilase should not be confused with nitrile hydratase which hydrolyses nitriles to amides. Nitrile hydratases are almost invariably co-expressed with an amidase, which converts the amide to the carboxylic acid. Consequently, it can sometimes be difficult to distinguish nitrilase activity from nitrile hydratase plus amidase activity.
Cysteine metabolism refers to the biological pathways that consume or create cysteine. The pathways of different amino acids and other metabolites interweave and overlap to creating complex systems.
In chemistry, a sulfenic acid is an organosulfur compound and oxoacid with the general formula R−S−OH. It is the first member of the family of organosulfur oxoacids, which also include sulfinic acids and sulfonic acids, respectively. The base member of the sulfenic acid series with R = H is hydrogen thioperoxide.
Nitrile hydratases are mononuclear iron or non-corrinoid cobalt enzymes that catalyse the hydration of diverse nitriles to their corresponding amides
Cystathionine-β-synthase, also known as CBS, is an enzyme (EC 4.2.1.22) that in humans is encoded by the CBS gene. It catalyzes the first step of the transsulfuration pathway, from homocysteine to cystathionine:
Cystathionine is an intermediate in the synthesis of cysteine.
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:
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.
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.
Cystathionine beta-lyase, also commonly referred to as CBL or β-cystathionase, is an enzyme that primarily catalyzes the following α,β-elimination reaction
The enzyme methionine γ-lyase (EC 4.4.1.11, MGL) is in the γ-family of PLP-dependent enzymes. It degrades sulfur-containing amino acids to α-keto acids, ammonia, and thiols:
In enzymology, a cystathionine gamma-synthase is an enzyme that catalyzes the formation of cystathionine from cysteine and an activated derivative of homoserine, e.g.:
In molecular biology, the Cys/Met metabolism PLP-dependent enzyme family is a family of proteins including enzymes involved in cysteine and methionine metabolism which use PLP (pyridoxal-5'-phosphate) as a cofactor.
Methionine sulfoxide is the organic compound with the formula CH3S(O)CH2CH2CH(NH2)CO2H. It is an amino acid that occurs naturally although it is formed post-translationally.
Mercury(II) reductase (EC 1.16.1.1), commonly known as MerA, is an oxidoreductase enzyme and flavoprotein that catalyzes the reduction of Hg2+ to Hg0. Mercury(II) reductase is found in the cytoplasm of many eubacteria in both aerobic and anaerobic environments and serves to convert toxic mercury ions into relatively inert elemental mercury.
