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Cysteine (/ ˈ s ɪ s t ɪ iː n /; [5] symbol Cys or C [6]) is a semiessential [7] proteinogenic amino acid with the formula HOOC−CH(−NH 2)−CH 2 −SH. The thiol side chain in cysteine enables the formation of disulfide bonds, and often participates in enzymatic reactions as a nucleophile. Cysteine is chiral, but both D and L-cysteine ...
Cystine is the oxidized derivative of the amino acid cysteine and has the formula (SCH 2 CH(NH 2)CO 2 H) 2.It is a white solid that is poorly soluble in water. As a residue in proteins, cystine serves two functions: a site of redox reactions and a mechanical linkage that allows proteins to retain their three-dimensional structure.
As the functional group of the amino acid cysteine, the thiol group plays a very important role in biology. When the thiol groups of two cysteine residues (as in monomers or constituent units) are brought near each other in the course of protein folding, an oxidation reaction can generate a cystine unit with a disulfide bond (−S−S−).
A variety of organosulfur compounds occur in nature. Most abundant are the amino acids methionine, cysteine, and cystine. The vitamins biotin and thiamine, as well as lipoic acid contain sulfur heterocycles. Glutathione is the primary intracellular antioxidant. [6] Penicillin and cephalosporin are life-saving antibiotics, derived from fungi.
Cysteic acid also known as 3-sulfo-l-alanine is the organic compound with the formula HO 3 SCH 2 CH(NH 2)CO 2 H. It is often referred to as cysteate, which near neutral pH takes the form − O 3 SCH 2 CH(NH 3 +)CO 2 −. It is an amino acid generated by oxidation of cysteine, whereby a thiol group is fully oxidized to a sulfonic acid/sulfonate ...
The complete data for Cysteine. General information. ... 2-amino-3-sulfanylpropanoic acid 3-mercaptoalanine AIDS{-}160777 CHEBI:15356 CHEMBANK2703 NSC 63864 NSC647530
The pI value can affect the solubility of a molecule at a given pH. Such molecules have minimum solubility in water or salt solutions at the pH that corresponds to their pI and often precipitate out of solution. Biological amphoteric molecules such as proteins contain both acidic and basic functional groups. Amino acids that make up proteins ...
The acid-base properties of the imidazole side chain are relevant to the catalytic mechanism of many enzymes. [10] In catalytic triads, the basic nitrogen of histidine abstracts a proton from serine, threonine, or cysteine to activate it as a nucleophile. In a histidine proton shuttle, histidine is used to quickly shuttle protons. It can do ...