Sulfonium compounds, protein

Methionine is utilized primarily in protein synthesis, providing sulfur for cysteine synthesis, and is the body s principal methyl donor. In methylation reactions, S-adenosylmethionine (SAM) is the methyl group donor. SAM is a sulfonium compound whose adenosyl moiety is derived from ATP as follows ... 

Various sulfonium compounds as substrate for the enzyme Various sulfonium compounds were tested for their ability as methyl donor for the carboxymethyl esterification of ACTH by the action of protein methylase II. As shown in Table I, besides the natural methyl donor, only S-adenosyl-L-(2-hydroxy-4-methylthio)-butyric acid showed a moderate activity. The other compounds were found to be inactive within the limits of accuracy of the analyti-cal test. 

SULFONIUM COMPOUNDS AS METHYL DONORS FOR PROTEIN METHYLASE II... 

The incubation mixture contained 25 yl of citrate-phosphate buffer, pH 6.0 (prepared by mixing 1 part of 0.5 M disodium phosphate and 0.6 part of 0.25 M citric acid), 2 mM EDTA, 50 yg of ACTH as methyl acceptor protein, 2 yg of purified protein methylase II and labeled sulfonium compounds at the indicated concentrations in a final volinne of 250 yl. The incubation was carried out for 10 min. at 37°C. 

Various sulfonium conq>ounds as inhibitors for the enzyme The sulfonium compounds were also examined for their inhibitory activity for protein methylase II in the presence of S-ade-... 

Analogs of metabolic intermediates have been widely used to investigate the mechanism of biochemical reactions. Along this line, a series of sulfonium compounds and thioethers, analogs of S-adeno-syl-L-methionine and S-adenosyl-L-homocysteine respectively have been assayed as substrate and/or inhibitors of methyltransfer reactions (33-36). However, these studies mainly concerned with methyltransferases acting on small molecules and tRNA (33-37). In this brief account, we have reviewed recent studies on the effect of afore-mentioned compounds on various protein-specific methyltransferases. 

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