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NADPH and NADH oxidoreductases may provide candidate sources of superozdde anions associated with cell survival and growth. Although a growing body of evidence supports the biological importance of the oxidoreductases, their biochemical properties has not been investigated systematically. In this study, we compared their enzymatic characters and kinetics in the PM isolated from bovine liver. Both oxidoreductases were highly specific to the plasma membrane and distinguished from other microsomsl and mitochondrial oxidases. A NADPH analog, 2´,5´-ADP specifically inhibited plasma membrane-associated NADPH oxidoreductase, suggesting that it is a good material to differentiate the enzyme from NADH oxidoreductases. The enzymes showed different elution profiles in Q-sepharose column. The NADPH oxidoreductases had a lower affinity to substrate whereas the difference of Vmax between the enzymes was not significant. Both enzyme activities were activated by the lipid reconstruction, which is the common property of plasma membrane enzymes. These results may provide good criteria to evaluate PM-associated oxidoreductases in tissues and cells, and to purify the oxidases from PM.
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