A critical examination of some histochemical methods for demonstrating tetrahydrofolate dehydrogenase

Synopsis Two different methods, one proposed by us (1969, 1970) and the other by Onicescuet al. (1970), for the histochemical demonstration of tetrahydrofolate dehydrogenase have been compared using as test materials frozen sections of mouse liver and blood smears of laboratory animals that had been infected experimentally with malaria.Our method appears to be of practical value, especially for blood smears. It is based on the following principles: (a) the enzymic reaction proceeds via the reduction of the pyridine coenzyme NADP by tetrahydrofolic acid (dissolved in 2-mercaptoethanol to prevent its spontaneous oxidation); (b) an intermediate electron carrier, phenazine methosulphate, is used to increase the reaction sensitivity; and (c) antifolate metabolic inhibitors are added in specificity controls.The differences between other methods, which have failed in our hands, and our method are discussed critically.Centre for the Study of Histochemistry of the C.N.R.