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The distribution and some properties of FAD-linked α-glycerophosphate dehydrogenase of human term placenta have been studied. Human placenta was fractionated by differential centrifugation into nuclear, mitochondrial and cytosolic fractions. The activity of mitochondrial FAD-linked α-glycerophosphate dehydrogenase(cytochrome oxidoreductase, EC 1.1.99.5) was measured by the procedure of Gonzalez-Cerozo and Dalziel. The activity in homogenate was found to be 33 units per g wet tissue and was recovered about 87% in mitochondrial fraction (specific activity: 2.02 units/mg protein). Cytosolic NAD-linked α-glycerophosphate dehydrogenase (NAD^+ 2-oxidoreductase, EC 1.1.1.8) activity was assayed by the method of Dawson and Thorne. The activity in homogenate was 25 units per g and was recovered about 96% in cytosolic fraction(specific activity: 0.57 units/mg protein). Thus, the specific activity of FAD-linked dehydrogenase in mitochondria was to be about 3.5-fold greater than that of NAD-linked dehydrogenase in cytosol. Mitochondrial FAD-linked α-glycerophosphate dehydrogenase from human placenta has been purified about 139-fold by osmotic shock, solubilization with Triton X-100, and DEAE-cellulose column chromatography. The optimal temperature for enzyme activity was 38℃ and the optimal pH was 7.6. The Km value for α-glycerophosphate was 9.34mM. The molecular weight was estimated to be 320,000±10,000 by polyacrylamide disc gel electrophoresis. The half life of the enzyme activity was 5 min at 50℃. At the concentration of 1.0×10^-4M of magnesium ion and clacium ion, the enzyme activities of α-glycerophosphate dehydrogenase were increased to 35% and 8%, respectively. However, at the greater concentration over 1.0×10^-4M of magnesium ion and calcium ion, the enzyme activities were markedly reduced.
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