The product, oxidized nicotinamide adenine dinucleotide phosphate (NADP+),formed following the reaction of NADK with NAD+ and adenosine 5′-triphosphate was detected with the aid of glucose-6-phosphate dehydrogenase or NADP+–isocitrate dehydrogenase, iodonitrotetrazolium chloride, and phenazine methosulfate.