THE ASSAY OF URIDINE DIPHOSPHOGLUCOSE DEHYDROGENASE-ACTIVITY - DISCRIMINATION FROM XANTHINE DEHYDROGENASE-ACTIVITY

The biochemical and quantitative cytochemical assays of the activity of uridine diphosphoglucose dehydrogenase (UDPG-D) have produced perplexing results. It is now shown that the perplexity may be due to the possibility that the coenzyme (NAD) required for UDPG-D activity, may be acting as a substrate for a second dehydrogenase, namely xanthine dehydrogenase, which may utilize NAD as its substrate. The activity of UDPG-D can be distinguished selectively by the pH of its optimal activity and by decreasing the concentration of the coenzyme used in the assay.