Abstract
ABSTRACTGlutamate dehydrogenase in Acanthamoeba castellanii is an NAD‐dependent cytosolic enzyme. This is similar to glutamate dehydrogenases in Phycomycetes, but very different from the dual coenzyme‐specific enzymes located in mitochondria in animals and in mitochondria and chloroplasts in higher plants. Pyrroline‐5‐carboxylate (P‐5‐C) reductase occurs also in the cytoplasm in A. castellanii and has very high affinities for L‐P‐5‐C (Km= 12 μM) and NADH (Km= 15 μM). In contrast, ornithine aminotransferase and proline oxidase are mitochondrial enzymes. No proline‐inhibited γ‐glutamyl kinase was detected while an active glutamine synthetase was found in the cytosolic compartment. Evidence for a mitochondrial transport system for L‐proline was obtained. Two possible pathways for proline biosynthesis in A. castellanii are discussed based on information obtained about activities and subcellular compartmentation of enzymes.
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