Enzymatic degradation of succinyl-coenzyme A by rat liver homogenates

When a dilute suspension of the mitochondrial fraction of rat liver homogenates was incubated with chemically synthesized succinyl-CoA, a product was rapidly formed which was retained at pH 3.9 on Dowex 50 (H+). Although its acid-base properties were indistinguishable from those of epsilon-aminolevulinic acid, the product did not form a pyrrole with acetylacetone, nor was its enzymatic formation dependent on added glycine. The enzyme which cleaved succinyl-CoA to the epsilon-aminolevulinic acid-like product was inhibited by phenylmethyl sulfonylfluoride. The first substance formed by the peptidase was the unstable thioester of succinic acid and cysteamine which underwent rearrangement to the more stable N-succinyl cysteamine above pH 4.0. It is apparent that the assay of epsilon-aminolevulinic acid synthetase (EC 2.3.1.37) by the ion-exchange method of Ebert et al. (Ebert, P.S., Tschudy, D.P., Choudhry, J.N. and Chirigos, M.A. (1970) Biochim. Biophys. Acta 208, 236--250) can yield erroneous results with succinyl-coenzyme A as substrate, especially when incubations are carried out for less than 25 min.