AN IMPROVED METHOD FOR THE HISTOCHEMICAL LOCALIZATION OF

An improved procedure is reported for the histochemical localization of glucose-fl- phosphate dehydrogenase in fresh-frozen sections of animal and plant tissues. Used in this procedure are an incubation medium and an inert high-molecular-weight polyvinyl alcohol as a stabilizer to check enzyme diffusion. The incubation medium consists of 10 mg each of nicotinamide adenine dinucleotide phosphate and nitroblue tetrazolium chloride and 60 mg of glucose-6-phosphate per 20 ml of 22% polyvinyl alcohol solution in 0.2 M Tris-maleate buffer, pH 7.2. Use of this medium has given consistent results with the tissues tested. Be'cause the use of an electron-transfer agent in the incubation medium often resulted in enzyme diffu- sion, its use in glucose-fl-phosphate dehydrogenase localization is considered undersirable. Incubation time of 15 to 30 mm for animal-tissue and 20 to 45 mm for plant tissue at 37#{176}C was found to be optimal for producing the characteristic blue formazan at the reaction sites.