Antimony biomethylation by Scopulariopsis brevicaulis: characterization ofintermediates and the methyl donor

The filamentous fungus Scopulauiopsis brevicaulis biomethylates inorganic a ntimony(III) compounds to trimethylstibine, that can be detected in culture headspace gases. Dimethylantimony and trimethylantimony species have been detected in the medium of these cultures, but the origin of these species w as controversial. We now show that the dimethylantimony species is a true i ntermediate on the pathway to trimethylstibine (rather than arising from tr imethylstibine oxidation or as an analytical artifact) because no dimethyla ntimony species are formed on trimethylstibine oxidation, as determined by using HG-GC-AAS. Furthermore, the dimethylantimony and trimethylantimony sp ecies can be separated, by using anion exchange chromatography, and so the dimethylantimony species is not an analytical artifact, formed during the h ydride generation process. The antimony biomethylation mechanism was furthe r probed by measuring incorporation of the methyl group, from (CD3)-C-13-L- methionine and CD3-D-methionine, into methylantimony species and, for compa rison, into methylarsenic species. The percentage incorporation of the labe led methyl group into methylarsenic and methylantimony species was not sign ificantly different. The incorporation from (CD3)-C-13-L-methionine was 54% and 47% for antimony and arsenic, respectively. The incorporation from CD3 -D-methionine was 20% and 16% for antimony and arsenic, respectively. It ap pears that the biomethylation of arsenic and antimony occur by very similar , perhaps identical, mechanisms. (C) 2000 Elsevier Science Ltd. All rights reserved.