Fumarylacetoacetic acid hydrolase

Fumarylacetoacetic acid hydrolase Fumaric acid + Acetoacetic acid... 

The next enzymic step in the dissimilation of tyrosine, oxidation of homogentisic acid, was clearly established by the work of Ravdin and Crandall 2H0). These investigators isolated two enzyme fractions from a rat liver homogenate, one of which catalyzed the oxidation of homogentisic acid to an open chain diketone-dicarboxylic acid. In their hands the product isolated was 4-fumarylacetoacetic acid. Subsequent work has shown that the initial product is 4-maleylacetoacetic acid and that an isomerase is present which converts this to the fumarylacetoacetate 221). The second enzyme of Ravdin and Crandall 220), fumarylacetoacetic acid hydrolase, hydrolytically cleaves this compound to fumarate and aceto-acetate. 

Fumarylacetoacetate is split to fumarate and acetoacetate by an enzyme that was known previously to hydrolyze diketo acids. It has been called acylpyruvase, triacetic acid hydrolyzing enzyme, and /J-diketonase. Since both the rate of hydrolysis of fumarylacetoacetate and its affinity for the enzyme exceed those of other substrates there is some justification for the name fumarylacetoacetate hydrolase. The irreversible action of this enzyme results in the formation of products that are metabolized by the systems previously described for fatty acid oxidation and the Krebs cycle. 

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