Mammalian metabolism of glutaric acid.

Rat liver mitochondria metabolize glutarate at a very slow rate as compared with glutaryl coenzyme A. The stimulatory effect of citric acid cycle intermediates, NAD, and coenzyme A on glutarate metabolism was interpreted as a manifestation of their involvement in the activation of glutarate by a thiol transferase with succinyl-Cob as the coenzyme A donor. Glutaryl-CoA dehydrogenase, which catalyzes the stoichiometric conversion of glutaryl-CoA to 1 mole each of carbon dioxide and crotonyl-CoA or its intermediate metabolite, was purified approximately 44and loo-fold from bovine liver and kidney mitochondria, respectively. The enzyme was shown to require an artificial electron acceptor and to be further stimulated by exogenous FAD. Of the various electron acceptors tested, methylene blue and phenazine methosulfate were most effective. The enzymes from both sources have similar properties. Catalysis was optimum at pH 7.5 in potassium phosphate buffer and at pH 8.0 in Tris-HCl buffer. The enzyme activity was inhibited by p-chloromercuribenzoate. The Ic, for glutaryl-CoA was 3.3 PM* Glutaconyl-CoA, the suspected primary intermediate of glutaryl-CoA metabolism, was synthesized, and its effect on the oxidation of glutaryl-CoA and its role as an alternative substrate for the partially purified enzyme were studied. Kinetic results indicated that glutaconyl-CoA competitively inhibited the release of 14COt from glutaryl-CoA-1,5-W possibly because of the metabolism of glutaconyl-CoA by the enzyme. Thus far, attempts to isolate enzymatically formed glutaconyl-CoA and to separate the dehydrogenation and decarboxylation activities of the enzyme have been unsuccessful.