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 different methyl-H-2(3)-labelled methyl precursors has been investigated, Both chloromethane (CH3Cl) and L-methionine caused earlier initiation of veratryl alcohol biosynthesis, but S-adenosyl-L-methionine (SAM) retarded the formation of the compound, A high level of (CH3)-H-2 incorporation into both the 3- and 4-O-methyl groups of veratryl alcohol occurred 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)] methionine was reduced by CH3Cl. These results suggest that L-methionine is converted either directly or via an intermediate to CH3Cl, which Is utilized as a methyl donor in veratryl alcohol biosynthesis, SAM is not an intermediate in the conversion of L-methionine to CH3Cl, In an attempt to identify the substrates for O methylation in the metabolic transformation of benzoic acid to veratryl alcohol, the relative activities of the SAM- and CH3Cl-dependent methylating systems on several possible intermediates were compared in whole mycelia by using isotopic techniques. 4-Hydroxybenzoic acid was a much better substrate for the CH3Cl-dependent methylation system than for the SAM-dependent system, The CH3Cl-dependent system also had significantly increased activities toward both isovanillic acid and vanillyl alcohol compared with the SAM-dependent system, On the basis of these results, it is proposed that the conversion of benzoic acid to veratryl alcohol involves para hydroxylation, methylation of 4-hydroxybenzoic acid, meta hydroxylation of 4-methoxybenzoic acid to form isovanillic acid, and methylation of isovanillic acid to yield veratric acid.