Biochemical studies on the enzymatic deficiencies in hereditary tyrosinemia

Experiments are described on the effects of succinylacetone and fumarylacetoacetate on delta-aminolevulinic acid dehydratase, methionine adenosyltransferase and p-OH-phenylpyruvate dioxygenase. delta-Aminolevulinic acid dehydratase from human erythrocytes is inhibited non-competitively by succinylacetone (Ki 0.03 mumol/l) and by fumarylacetoacetate (Ki 0.06 mumol/l). The inhibition by succinylacetone is not prevented by dithiothreitol, but the inhibition by fumarylacetoacetate is not observed if dithiothreitol is present. Methionine adenosyltransferase, partially purified from rabbit liver, is not inhibited by succinylacetone but is inhibited by fumarylacetoacetate: 69% inhibition is observed at 1 mmol/l. Human liver p-OH-phenylpyruvate dioxygenase is not inhibited by succinylacetone or fumarylacetoacetate. It is concluded that secondary enzyme deficiencies observed in hereditary tyrosinemia (delta-aminolevulinic acid dehydratase, methionine adenosyl transferase) are the result of inhibition by succinylacetone and fumarylacetoacetate, accumulating as a result of a primary deficiency of fumarylacetoacetase.