Dihydrofolic Reductase in Human Blood Cells

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Abstract
Dihydrofolic reductase assays were carried out according to 2 different procedures. The direct assay, based on the disappearance of NADPH2 at 340 nm, was suitable for purified preparations only, while the indirect method was satisfactory in crude lysates of leukocytes also. Intracellular amount of amethopterin was determined, after extraction, by the percentage inhibition of a partially purified preparation of chicken liver dihydrofolic reductase. This procedure is feasible owing to a stoichiometric binding, between enzyme and inhibitor, under the experimental conditions.