The metabolism of propionate in the colourless alga, Prototheca zopfii

Abstract

Propionate oxida-tion by washed whole cells of P. zopfii was inhibited by arsenite with accumulation of [alpha] -oxoglutaric acid and malonic semialdehyde. When fortified cell extracts metabolized [C14]propionate only 1 radioactive compound, [beta]-hydroxypropionate, was detected. In similar experiments with [2-C14]propionate, however, [beta]-hydroxypropionate, aspartate, glutamate, citrate, malate and an unidentified compound were all labelled. The addition of unlabelled glyoxylate or isocitrate to fortified extracts metabolizing [2-C14] -propionate increased the proportion of label incorporated into malate. Isocitrate lyase and malate synthase were found in extracts of propionate-grown cells. Experiments with cell-free extracts showed that the reactions of the malonic semialdehyde pathway could account for the conversion of propionate into acetyl-CoA. The malonic semialdehyde oxidative-decarboxylation system is inhibited by arsenite.