An Evaluation of the Histochemical Demonstration of Certain Pyridine Nucleotide-linked Dehydrogenases

Abstract

Farber, Sternberg and Dunlap^1,2 have questioned the validity of histochemical techniques for the demonstration of pyridine nucleotide-linked dehydrogenases. They have argued that since the actual reduction of the tetrazole results from its interaction not with a dehydrogenase but with a diaphorase (tetrazole reductase) specific for NADH or NADPH, strictly speaking the reactions are specific only for NADH- or NADPH-tetrazole reductase. Qualitative evidence was presented to show that of five pyridine nucleotide-linked dehydrogenases studied in rat kidney, only two staining patterns emerged, depending on whether the dehydrogenase required NAD⁺ or NADP⁺ in the reaction medium. While admitting that the tetrazole reductase was responsible for the actual reduction of tetrazole at the expense of reduced pyridine nucleotide, other workers^3,4 have concluded from similar experiments that each dehydrogenase has its own characteristic pattern of distribution. This point of view has been extensively accepted, but anomalies of formazan localization within the cell^5,6 and the observed escape of soluble dehydrogenases into the incubation medium^7–12 support the original conclusions of Farber and his colleagues.