Effects of Acid Catabolites on Activity in-vitro of Phenylalanine Hydroxylase from Rat Liver

SummaryThe activity of phenylalanine hydroxylase from rat liver can be inhibited in vitro by several organic acids including a few catabolites of phenylalanine, e.g., phenyl-pyruvate and homogentisate. However, the concentrations of such compounds necessary to produce significant inhibition of a generally competitive nature is far in excess of physiological amounts, and the effects can be minimized when an adequate amount of pteridine cofactor is present. Thus, the lowered activity of hydroxylase measured in experimental phenylketonuria may be attributed to a real suppression of enzyme synthesis, rather than inhibition by catabolites.