[The dynamics of the properties of liver phenylalanine hydroxylase in human embryogenesis].

Content, subunit composition and activity of phenylalanine hydroxylase's (PH) (EC 1.14.16.1) in cytoplasmic and membrane proteins extract of embryonic liver on week 6-11 of pregnancy were studied. PH enzymatic and antigenic activities were detected starting from the week 6 of pregnancy. Liver cytoplasmic PH antigen content increased gradually during development while its enzymatic activity remained practically unchanged. Concomitantly, relative content of L-subunit increased. Content of liver membrane PH antigen was constant during development. Samples of liver with relatively low specific PH activity were characterized by high content of PH in cytoplasm and vice versa. Since PH activity in extracts prepared from mixture of these samples decreased, an unknown PH inhibitor must be present in cytoplasmic protein extracts with relatively low specific PH activity.