Methionine biosynthesis in Candida albicans. I. S-Adenosyl-L-methionine (or S-methyl-L-methionine): homocysteine methyltransferase in cell-free extracts from yeast-like cells

Abstract

Six isolates of C. albicans were tested for their capacities to form methionine via S-adenosyl-L-methionine (or S-methyl-L-methionine): homocysteine methyltransferase (EC. 2.1.1.e). Cell-free extracts from all organisms were obtained from cultures containing predominantly (greater than 85%) yeast-like cells. Assay conditions with respect to pH, time of incubation, substrate, and protein concentrations for the methyltransferase reaction were determined.Extracts from all six strains formed methionine when either L-homocysteine, L-homocysteine thiolactone, or L-homocystine was used as the methyl acceptor, and more methionine was synthesized when S-methyl-L-methionine was the methyl donor than when S-adenosyl-L-methionine was used. The methyltransferase reaction was inhibited by methionine, L-methionine-ethyl-ester, and DL-N-hydroxy-methyl-methionine. Substantially less inhibition was observed with L-ethionine and S-methyl-L-cysteine, while no inhibition occurred when six other methionine analogs were tested.