ISOZYME HISTOCHEMISTRY, ESPECIALLY IN RELATION TO MALIGNANT TRANSFORMATION AND DIFFERENTIATION: I. HISTOCHEMICAL DEMONSTRATION OF LACTIC DEHYDROGENASE ISOZYMES

An idea of histochemical differential demonstration of the lactic dehydrogenase isozymes has been introduced and its procedures have been described. Inhibition of the activities of each lactic dehydrogenase isozyme subunit at the substrate, coenzyme, and enzyme levels by various kinds of chemicals and by physical conditions was investigated. Nicotinamide-hypoxanthine dinucleotide, an NAD analog, guanidine hydrochloride, urea, and heat were found to be useful for this purpose. The basic data and histochemical results are given, and the mechanisms involved are discussed. 1) The activity of H-type LDH is histochemically demonstrable in tissues by applying NHXD, an NAD analog, in place of NAD, or by adding guanidine hydrochloride or urea in the standard incubation medium. 2) The activity of M-type LDH is also histochemically demonstrable in tissue by pretreating the frozen, air-dried tissue sections through hot water at 60°. 3) These methods were verified by a biochemical analysis using agar-gel electrophoresis conducted in parallel. 4) All the possibilities for developing histochemical techniques for demonstrating the LDH isozyme subunits were discussed.