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Cysteine (symbol Cys or C; [5] / ˈ s ɪ s t ɪ iː n /) [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 ...
The complete data for Cysteine. General information. Chemical formula: C 3 H 7 N O 2 S ...
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.
See Amino acid for the pK a values of all amino acid side chains inferred in such a way. There are also numerous experimental studies that have yielded such values, for example by use of NMR spectroscopy. The table below lists the model pK a values that are often used in a protein pK a calculation, and contains a third column based on protein ...
The value for Arg is from Pace et al. (2009). [7] The value for Sec is from Byun & Kang (2011). [8] N.D.: The pKa value of Pyrrolysine has not been reported. Note: The pKa value of an amino-acid residue in a small peptide is typically slightly different when it is inside a protein.
Selenocysteine is an analogue of the more common cysteine with selenium in place of the sulfur. Selenocysteine is present in several enzymes (for example glutathione peroxidases , tetraiodothyronine 5′ deiodinases , thioredoxin reductases , formate dehydrogenases , glycine reductases , selenophosphate synthetase 2 , methionine- R -sulfoxide ...
Nitric acid, with a pK value of around −1.7, behaves as a strong acid in aqueous solutions with a pH greater than 1. [23] At lower pH values it behaves as a weak acid. pK a values for strong acids have been estimated by theoretical means. [24] For example, the pK a value of aqueous HCl has been estimated as −9.3.
It is a homologue of the amino acid cysteine, differing by an additional methylene bridge (-CH 2-). It is biosynthesized from methionine by the removal of its terminal C ε methyl group. In the body, homocysteine can be recycled into methionine or converted into cysteine with the aid of vitamin B 6, B 9, and B 12. [3]