Biosynthesis of Chloromethane in Phellinus pomaceus

Abstract

Summary: The effects of l- and d-methionine on production of the gaseous secondary metabolite chloromethane (CH3C1) by the white-rot fungus Phellinus pomaceus were investigated. Although d-methionine stimulated CH3C1 biosynthesis, the l-isomer either failed to affect or depressed production depending on the concentration. Nevertheless, very high levels of incorporation of label (~80%) from l-[methyl-2H3]methionine into CH3C1 could be achieved demonstrating that the amino acid is a highly effective precursor of CH3C1. Experiments using labelled d-methionine showed substantial but lower incorporation. Patterns of incorporation of label from both isomers into methyl benzoate, another important volatile fungal metabolite, were very similar to those observed with CH3C1. This behaviour is only explicable in terms of either (a) the utilization of the same enzyme system requiring an identical methyl donor for methylation of both chloride and benzoate ions or (b) the presence of a transmethylation system. The incorporation of label from l-[methyl-2H3]methionine into methyl 2-furoate was similar to that of methyl benzoate implying that the same methylating system was used for esterification of both 2-furoic and benzoic acids. However, the incorporation pattern for methyl salicylate was different and suggests that methyl salicylate is probably formed by o-hydroxylation of methyl benzoate.