[Presence of active phenylalanine hydroxylase in human leukocytes].

In homogenates of human leukocytes phenylalanine hydroxylase activity was shown to depend on concentration of protein, presence of specific hydroxylase inhibitors as well as on a dose of Ph+ gene; Km value was estimated for phenylalanine and cofactor. The data obtained suggest that human leukocytes contain membrane-bound phenylalanine hydroxylase, which is active in vitro and is similar apparently to the liver enzyme in its properties. Solubilization of the enzyme was achieved without alteration in its activity when 0.25% of Triton X-100 was added by cell homogenisation. Activity of phenylalanine hydroxylase in leukocytes was estimated by a modified procedure of tuling et al. The distinct discrimination between activity of phenylalanine hydroxylase obtained in groups of healthy persons as well as in homo- and heterozygotes by the Ph gene enabled to detect phenylketonuria and to reveal heterozygotes using leukocytes instead of liver tissue biopsy.