Aldehyde oxidation in human placenta. Purification and properties of 1-pyrroline-5-carboxylate dehydrogenase.
The human placenta contains a considerable amount of 1-pyrroline-5-carboxylate dehydrogenase (23 +/- 6 micrograms/g; n = 12), about 25% of the concentration present in liver. The enzyme is the only form 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 of enzyme can be obtained with a 12% yield. Placental 1-pyrroline-5-carboxylate dehydrogenase is a dimer of Mr-63,000 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 degrees C or after 23 min at 25 degrees C. It is irreversibly inhibited by disulfiram, and a molar ratio inhibitor: enzyme of 60:1 produced 50% inhibition 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.
Farrés
J
J
Departament de Bioquimica i Biologia Molecular, Facultat de Ciències, Universitat Autònoma de Barcelona, Bellaterra, Spain.
Julià
P
P
Parés
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X
D050842:1-Pyrroline-5-Carboxylate Dehydrogenase; D000447:Aldehydes / Q000378:metabolism*; D004221:Disulfiram / Q000494:pharmacology; D004592:Electrophoresis, Starch Gel; D004795:Enzyme Stability; D006801:Humans; D007700:Kinetics; D010084:Oxidation-Reduction; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000037:antagonists & inhibitors / Q000302:isolation & purification* / Q000378:metabolism; D010920:Placenta / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology
D000447:Aldehydes; D050842:1-Pyrroline-5-Carboxylate Dehydrogenase; C494240:ALDH4A1 protein, human; D000587:Oxidoreductases Acting on CH-NH Group Donors; D004221:Disulfiram