COMPARISON OF THE EFFICACIES OF CHLOROMETHANE, METHIONINE, AND S-ADENOSYLMETHIONINE AS METHYL PRECURSORS IN THE BIOSYNTHESIS OF VERATRYL ALCOHOL AND RELATED-COMPOUNDS IN PHANEROCHAETE-CHRYSOSPORIUM

The effect on veratryl alcohol production of supplementing cultures of the lignin-degrading fungus Phanerochaete chrysosporium with differen t methyl-H-2(3)-labelled methyl precursors has been investigated, Both chloromethane (CH3Cl) and L-methionine caused earlier initiation of v eratryl alcohol biosynthesis, but S-adenosyl-L-methionine (SAM) retard ed the formation of the compound, A high level of (CH3)-H-2 incorporat ion into both the 3- and 4-O-methyl groups of veratryl alcohol occurre d when either L-[methyl-H-2(3)] methionine or (CH3Cl)-H-2 was present, but no significant labelling was detected when S-adenosyl-L-[methyl-H -2(3)] methionine was added, Incorporation of (CH3)-H-2 from (CH3Cl)-H -2 was strongly antagonized by the presence of unlabelled L-methionine ; conversely, incorporation of (CH3)-H-2 from L-[methyl-H-2(3)] methio nine was reduced by CH3Cl. These results suggest that L-methionine is converted either directly or via an intermediate to CH3Cl, which Is ut ilized as a methyl donor in veratryl alcohol biosynthesis, SAM is not an intermediate in the conversion of L-methionine to CH3Cl, In an atte mpt to identify the substrates for O methylation in the metabolic tran sformation of benzoic acid to veratryl alcohol, the relative activitie s of the SAM- and CH3Cl-dependent methylating systems on several possi ble intermediates were compared in whole mycelia by using isotopic tec hniques. 4-Hydroxybenzoic acid was a much better substrate for the CH3 Cl-dependent methylation system than for the SAM-dependent system, The CH3Cl-dependent system also had significantly increased activities to ward both isovanillic acid and vanillyl alcohol compared with the SAM- dependent system, On the basis of these results, it is proposed that t he conversion of benzoic acid to veratryl alcohol involves para hydrox ylation, methylation of 4-hydroxybenzoic acid, meta hydroxylation of 4 -methoxybenzoic acid to form isovanillic acid, and methylation of isov anillic acid to yield veratric acid.