Mechanism of l-serine oxidation in Entamoeba histolytica

Abstract

1. 1. The enzymatic mechanism of oxygen uptake elicited by l-serine in axenically cultivated trophozoites of Entamoeba histolytica was investigated. 2. 2. Of 22 amino acids examined, only l-serine stimulated oxygen consumption by intact and disrupted amoebae. 3. 3. Pyruvate, a product of serine metabolism, also stimulated oxygen consumption in the amoebae. 4. 4. Characterization of the oxygen uptake elicited by both l-serine and pyruvate, and analysis of the products of l-serine metabolism indicate that the amino acid is first converted to pyruvate. 5. 5. l-Serine dehydratase, which catalyzes the deamination of serine to pyruvate, was detected primarily in the soluble fraction of the amoebae. d-Serine potently inhibited the enzyme, as well as oxygen uptake in the presence of l-serine but not in the presence of pyruvate. 6. 6. The pyruvate formed is oxidized, at least in part, by a novel pyruvate oxidase involving the uptake of molecular oxygen.