title: 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.
mesh_terms: D001152:Arsenicals / Q000096:biosynthesis*; D002175:Candida / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation; D013696:Temperature
chemical_list: D001152:Arsenicals; D003513:Cycloheximide; C009572:trimethylarsine