The metabolism of acetate in the colourless alga, Prototheca zopfii

Abstract

Evidence is presented for the existence of the tricarboxylic acid cycle as the major pathway for the oxidation of acetate in Prototheca zopfii. Whole cells did not oxidize intermediates of the cycle at neutral pH, but disruption of a cell envelope by grinding with carborundum gave a preparation that slowly oxidized fumarate, succinate, [alpha]-oxoglutarate, and citrate. The oxidation of acetate by whole cells was inhibited by fluoroacetate and arsenite; [alpha]-oxoglutarate, produced from acetate by whole cells in the presence of arsenite, was readily detected. The following enzymes were shown to be present; the acetate-activating enzyme, citrate synthase, aconitate hydratase, isocitrate dehydro-genase, succinate dehydrogenase, fumarate hydratase, and malate dehydrogenase. Enzymes directly tested for and not found are glutamate dehydrogenase, [alpha]-alanine dehydrogenase, asparatase and [alpha]-oxoglutarate dehydrogenase; indirect evidence for the presence of the last-named enzyme was obtained. Acatete-grown cells contained isocitrate lyase and malate synthase; isocitrate lyase was inducible and not present in cells grown with glucose. Both enzymes occurred principally in the fraction that was sedimented in 10 minutes at 1000g.