Aldehyde oxidation in human placenta. Purification and properties of 1-pyrroline-5-carboxylate dehydrogenase

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Abstract
The human placenta contains a considerable amount of 1-pyrroline-5-carboxylate dehydrogenase (23 .+-. 6 .mu.g/g;n=12), about 25% of the concentration present in liver. The enzyme is the only from in placenta that oxidizes short- and medium-chain aldehydes, which facilitates its purification from this organ. It can be purified to homogeneity by successive chromatographies on DEAE-cellulose, 5''-AMP-Sepharose and Sephacryl S-300. From 500 g of tissue, about 2.1 units enzyme can be obtained with a 12% yield. Sephacryl S-300. From 500 g of tissue, about 2.1 units of enzyme can be obtained with a 12% yield. Placental 1-pyrroline-5-carboxylate dehydrogenase is a dimer of Mr-63000 subunits. It exhibits a pI of 6.80-6.65, and is specific for 1-pyrroline-5-carboxylate, the cyclic form of glutamate .gamma.-semialdehyde (Km = 0.17 mM, Kcat. = 870 min-1), although it also oxidizes short-chain aliphatic aldehydes such as propionaldehyde (Km = 24 mM, kcat. = 500 min-1). These properties are very close to those of the liver enzyme, indicating a strong similarity between the enzyme forms from both organs. The enzyme is highly sensitive to temperature, showing 50% inhibition after incubation for 0.8 min at 45.degree.C or after 23 min at 25.degree.C. It is irreversibly inhibited by disulfiram, and a molar ratio inhibitor: enzyme of 60: 1 produced 50% inhbition after incubation for 10 min. A subcellular-distribution study indicates that the enzyme is located in two compartments: the mitochondria, with 60% of the total activity, and the cytosol, with 40% activity. The physiological role of the enzyme in placental amino acid metabolism is discussed.