Studies on the molecular defect in phenylketonuria and hyperphenylalaninaemia using antibodies against phenylalanine hydroxylase.

Monospecific antibodies against human phenylalanine hydroxylase were prepared. Liver extract of 10 patients with phenylketonuria (PKU) and of two patients with hyperphenylalaninaemia were examined for reactivity toward the antibodies in crossed immunoelectrophoresis. In all patients phenylalanine hydroxylase could be detected. In nine out of 10 patients with PKU the mutant enzyme did not differ from the wild type enzyme with respect to the electrophoretic mobility. In one case the mutant enzyme had a more negative charge. In the patients with hyperphenylalaninaemia the enzyme of one patient had normal electrophoretic mobility and the enzyme of the other differed from the normal enzyme. No difference could be shown in heterozygotes for PKU.