The reduction of trimethylarsine oxide by Candida humicola

Abstract

Trimethylarsine oxide, a probable intermediate in the biological transformation of arsenate, was reduced to volatile trimethylarsine by Candida humicola. A simple assay for the rate of trimethylarsine production from trimethylarsine oxide by the fungus was developed. The optimum pH for the reduction was determined as 5.1-5.2, and the optimum temperature was 40 degrees C. The rate of reduction was directly proportional to cell concentration and followed Michaelis-Menten type kinetics. There was almost no trimethylarsine produced by heated or broken cells. The reaction was inhibited by a number of electron transport inhibitors and uncouplers of oxidative phosphorylation including cyanide, azide, and 2,4-dinitrophenol. The rate of reduction was modified by arsenate, methylarsonate, dimethylarsinate, selenate, and tellurate. Preincubation of cells with trimethylarsine oxide increased the rate of reduction 69-fold; this increase in activity was blocked if the cells were incubated with the protein synthesis inhibitor cycloheximide.

Bioaccumulation and excretion of arsenic compounds by a marine unicellular alga, polyphysa peniculus

“…The reduction may be enzymic or it could occur chemically by reaction of arsenate with an enzymatically produced reducing agent. 34 Regardless of which mechanism is correct, the results show that it is necesary to have a biologically intact organism capable of generating the appropriate reducing conditions, because nonmetabolizing, enzymically inactive cells do not reduce arsenate to arsenite in the growth medium.…”

Microbial Methylation of Metalloids: Arsenic, Antimony, and Bismuth

“…Only a brief account will be given here since two authoritative reviews are available (52,75). All of the organic As(V) compounds of the Challenger pathway (methylarsonate, dimethylarsinate, trimethylarsine oxide) have been observed in cell extracts metabolizing arsenate, and all of them are precursors for trimethylarsine biosynthesis (70,195). Preconditioning of cells with dimethylarsinate improves trimethylarsine formation from arsenate and dimethylarsinate.…”

“…humiculus was known to reduce trimethylarsine oxide to trimethylarsine (195), and this oxide was also reduced under both aerobic and anaerobic conditions by several bacteria (194 subtilis, E. coli, S. aureus (grown aerobically), and two unidentified skin aerobes. A further skin aerobe and Streptococcus sanguis were much less active.…”

Confirmation of the aerobic production of trimethylstibine by Scopulariopsis brevicaulis

“…10 At higher concentrations trimethylarsine oxide is readily reduced by S. brevicaulis to trimethylarsine. 11 The culture containing trimethylantimony dichloride (1 mg Sb ml À1 ) produced approximately six times more trimethylstibine than the cultures containing potassium antimony tartrate (1000 mg Sb ml À1 ). The low production of trimethylstibine, in cultures containing 1000 mg Sb ml À1 , is probably a result of low rates of biomethylation.…”