1887

Abstract

Summary: The kinetics of carboxylic acid methylation by chloromethane (CHCl) in mycelia of the fungus were examined. Substantial incorporation of CH- into ester was observed within 5 min of addition of CHCl to washed mycelia in the presence of the non-physiological acceptor butyric acid, rendering it unlikely that CHCl was converted to a diffusible intermediate before acting as methyl donor. The rate of methyl butyrate biosynthesis attained a maximum of 0·14 μmol g h at 1·5 mM-butyric acid, with higher concentrations causing increasing inhibition. Exogenous CHCl did not affect methyl butyrate production implying that the rate of CHCl biosynthesis did not limit methylation. However, CH,-incorporation from exogenous CHCl into methyl butyrate rose sharply from 20 to 60% between 1·5 and 4 mM-butyric acid, suggesting inhibition of CHCl biosynthesis by the acid, an interpretation supported by the rapid decline in gaseous CHCl release by mycelia between 1·5 and 2 mM-butyric acid. With the natural acceptor benzoic acid as substrate a significant increase in the rate of ester biosynthesis was obtained in the presence of exogenous CHCl. Ester biosynthesis was maximal (0·18 μmol g h) at 0·5 mM-benzoic acid but fell extremely rapidly with increasing concentration. As with butyric acid supraoptimal concentrations halted CHCl release and increased CH-incorporation from exogenous CHCl. Studies on CH-incorporation from exogenous CHCl into ester revealed a linear relationship between the logarithm of the percentage CH-incorporation and the logarithm of CHCl concentration with both butyric and benzoic acids as substrate, suggesting that exogenous CHCl competed with endogenously synthesized CHCl for adsorption at a solid interface, possibly a membrane within the cell, prior to reaction of the compound at the active site. When mycelia were grown in the presence of different halide ions, greater methylating activity was found in Br- and I-grown mycelia. The system had a higher affinity for CHBr and CHI as methyl donors than CHCl. Fluoromethane was not a substrate for the methylating system nor did it act as a competitive inhibitor.

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/content/journal/micro/10.1099/00221287-136-8-1509
1990-08-01
2019-10-14
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http://instance.metastore.ingenta.com/content/journal/micro/10.1099/00221287-136-8-1509
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