Evidence for the existence of independent chloromethane- and S-adenosylmethionine-utilizing systems for methylation in Phanerochaete chrysosporium

Abstract

O methylation of acetovanillone at 4 position by C2H3Cl and S-adenosyl[methyl-2H3]methionine was monitored in whole mycelia of Phanerochaete chrysosporium in the presence and absence of S-adenosylhomocysteine. Both the amount of the methylation product, 3,4-dimethoxyacetophenone, and the percent C2H3 incorporation into the 4-methoxyl group of the compound were determined. The results strongly suggest the presence of biochemically distinct systems for O methylation of acetovanillone utilizing S-adenosylmethionine and chloromethane, respectively, as the methyl donor. The S-adenosylmethionine-dependent enzyme is induced early in the growth cycle, with activity attaining an initial maximum after 55 h of incubation. Methylation by this enzyme is totally suppressed by 1 mM S-adenosylhomocysteine over almost the entire growth cycle. S-Adenosylmethionine-dependent O-methyltransferase activity is detectable in cell extracts, and the purification and characterization of the enzyme are described elsewhere (C. Coulter, J. T. Kennedy, W. C. McRoberts, and D. B. Harper, Appl. Environ. Microbiol. 59:706-711, 1993). The chloromethane-utilizing methylation system is absent in early growth but attains peak activity in the mid-growth phase after 72 h of incubation. The system is not significantly inhibited by S-adenosylhomocysteine at any stage of growth. No chloromethane-dependent O-methyltransferase activity is detectable in cell extract, suggesting that the enzyme is membrane bound and/or part of a multienzyme complex. Although the biochemical role of the chloromethane-dependent methylation system in metabolism is not known, one possible function could be the regeneration of veratryl alcohol degraded by the attack of lignin peroxidase.