Biosynthesis of Dimethylsulfoniopropionate in Crypthecodinium Cohnii (Dinophyceae)
Dimethylsulfoniopropionate(DMSP) is the precursor of dimethylsulfide (DMS) which is the most abundant volatile sulfur compound in sea water. Various marine macroalgae and microalgae contain DMSP in high concentration and release DMS. Crypthecodinium cohnii (Dinophyceae) is one of the DMSP producers. In C. cohnii, the sulfur, the methyl carbon and carbons 2 and 3 of the methionine molecule are efficiently incorporated into DMSP. The location of label in the radioactive DMSP is consistent with the conversion of methionine to DMSP by decarboxylation, deamination, and methylation. Methionine incorporation into DMSP was not inhibited in the presence of methionine-related compounds such as S-methylmethionine and S-adenosylmethionine. Methionine incorporation into DMSP was completely inhibited in the presence of methylmercaptopropionic acid but was not inhibited by methylthiooxybutanoic acid. These data are consistent with a biosynthetic pathway in which methionine is first decarboxylated to methylthiopropylamine. This is followed by loss of the amino group and oxidation to give methylmercaptopropionic acid, which is subsequently methylated. Methionine decarboxylase, which may be the key enzyme of biosynthesis of DMSP, was purified from C. cohnii and characterized. This enzyme is pyridoxalphosphate-dependent. The N-terminal amino acid sequence of this enzyme is Ala-Leu-Cys-Trp-Ser-Asp-Ile-Ser-Pro—.
KeywordsCellulose Phytoplankton Cysteine Polypeptide Dimethyl
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