[Dihydropteridine reductase activity in leukocytes and cultured fibroblasts of health individuals and of patients with the classical form of phenylketonuria].

Activity of dihydrohypteridine reductase, estimated by means of spectrophotometric method, was found in cell culture of human fibroblasts and in leukocytes of peripheric blood. The enzymatic activity was not altered markedly with time; thus suggesting a possibility to classify dihydropteridine reductase as a constitutive enzyme. In patients with typical form of phenylketonuria the enzymatic activity tended to decrease as compared with healthy persons.