Determination of NADPH-specific dihydropteridine reductase in extract from human, monkey, and bovine livers by single radial immunodiffusion: selective assay differentiating NADPH- and NADH-specific enzymes.

It has been difficult to determine exactly NADPH-specific dihydropteridine reductase [EC 1.6.99.10] in samples which also contain NADH-specific dihydropteridine reductase [EC 1.6.99.7], because the latter enzyme interferes with the activity measurement of the former. We have devised a method to measure selectively the NADPH-specific reductase in crude extracts of bovine, human and monkey livers by the single radial immunodiffusion method using specific antiserum against the enzyme. This method makes it possible to determine the enzyme amount in 5 microliters of the 3-volume extracts of the livers. The amounts of NADPH-specific dihydropteridine reductase were calculated to be 0.252, 0.296, and 0.583 munits/5 microliter of the extracts of bovine, human, and monkey livers, respectively.