Lack of Citrate Lyase — the Key Enzyme of the Reductive Carboxylic Acid Cycle — in Chlorobium thiosulfatophilum and Rhodospirillum rubrum

Abstract

Extracts of Chlorobium thiosulfatophilum and of Rhodospirillum rubrum have been tested for the presence of citrate lyase under various conditions. This enzyme could not be detected. It is, therefore, concluded that a complete reductive carboxylic acid cycle does not occur in these microorganisms. The enzymes required for a-ketoglutarate synthesis from oxaloaetate and acetyl-coenzyme A are present in autotrophically grown cells of C. thiosulfatophilum and R. rubrum. This supports the view that a reaction sequence catalyzing the conversion of α-ketoglutarate into oxaloacetate is unlikely to exist in these bacteria.