Methionine synthesis in Ochromonas malhamensis

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Abstract
Both resting cells and cell-free extracts of Ochromonas malhamensis grown in a vitamin Bl2-containing medium are capable of methionine synthesis. Optimum conditions of pH and reaction time, as well as the relative contribution of various precursors in the formation of the methyl moiety, have been ascertained. The decrease of methionine-synthesizing activity of the cell-free extract caused by Dowex 2 (Cl''form) treatment was restored completely on addition of heat-inactivated cell-free extract and partially by adenosine triphosphate. The fraction obtained by 25-50% saturation with ammonium sulphate of the cell-free extract caused optimum synthesis of methionine in the presence of heat-inactivated cell-free extract or dialysed, heat-inactivated cell-free extract together with a cofactor mixture whose active components were adenosine triphosphate, diphosphopyridine nucleotide and magnesium sulphate. Cell-free extracts of the micro-organism grown in a methionine-containing medium in the absence of vitamin B12 only synthesized methionine in the presence of heated extracts of cells grown with the vitamin. Dimethylbenzimidazole-vitamin B12 coenzyme did not replace the heated extract.