An interpretation of human diaphorase isozymes in terms of three gene loci DIA1, DIA2 and DIA3.

NADH and NADPH diaphorase isozymes have been studied in human tissues. Evidence from rare heterozygotes suggests that the red cell and main tissue forms of NADH diaphorase are products of the same locus DIA1. NADPH-dependent diaphorase appears to be the product of a second locus DIA2. A third locus, DIA3, codes for the polymorphic sperm diaphorase. The products of this locus are also found in foetal tissues including placenta and adult brain and gonads. The products of these three loci may be distinguished by their substrate specificity, thermostability and molecular size.