Production and requirements of S-containing amino acids

The more complex sulphur requirements of the marine animals are met largely by cysteine, cystine, methionine, biotin, and thiamine (Young and Maw, 1958) (Fig. 4). Cysteine is a component of the tripeptide glutathione and a precursor of taurine. Methionine is as an essential amino acid involved in biosynthesis of proteins, creatine and adrenaline. Adenosylmethionine is considered to be the active part in transmethylation, e.g. of choline. Methionine is part of the pathways to homocysteine, cystathionine and methylthioadenosine (Young and Maw, 1958). Various organisms convert cysteine and/or cystine into mercapturic acids, cysteine sulphinic acid, and thiazolidine derivatives (Zobell, 1963). 

From the extensive literature on amino acids as intermediate products of protein decomposition only a few papers, which include S-containing amino 

In certain organisms, e.g. the non-photosynthetic diatom Nitzschia alba, lecithine was found to be replaced by its sulphonium analogue (a phos-phatidyl-S,S-dimethylmercaptoethanol) as cell membrane component (Anderson et al., 1976) it was concluded that S-containing amino acids (e.g. cysteine, methionine) rather than serine probably act as primary precursors of the glycerophospholipids and sphingolipids which are involved in the formation of hydrophobic layers in membrane structures. 

Based on their DMS determinations in air and oceanic waters, of the emission of DMS from marine algae and soils. Lovelock et al. (1972) concluded that DMS may fulfill the role in the global sulphur cycle (providing a vehicle for the transfer of sulphur from the sea through air to the land surface) that 

As a photochemical oxidation product of DMS (Bentley et al., 1971) dimethyl sulphoxide may be detected in seawater which has been reported to inhibit photosynthesis in algae (Cheng et al., 1972). Methionine and biotin sulphoxides are oxidation products of methionine and biotin respectively, while microorganisms have been reported which reduce these compounds as well as DMDS (Zinder and Brock, 1978b). These authors also comment on the chemical stability of the sulphones. The methyl sulphones which have been identified in Baltic seal by Jensen and Jansson (1976) are, however, metabolically produced from PCB and DDE within the animal. 

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