Aromatization of cyclohexanecarboxylic acid.

An enzyme which catalyzes the aromatization of cyclohexanecarboxyl coenzyme A has been isolated from whole liver as well as from liver mitochondria. Incubation of the soluble, partially purified enzyme with cyclohexanecarboxyl-CoA produces cyclohexene-l-carboxyl-CoA, benzoyl-CoA, and a polar compound which has not. been further characterized. All three isomers of cyclohexenecarboxyl-CoA are converted to benzoyl-CoA by the liver enzyme, but evidence is presented indicating that only cyclohexene-l-carboxvl-CoA lies on the path from cyclohexanecarboxyl-CoA to benzoylCoA. Aromatization takes place either in air or anaerobically in the presence of artificial electron acceptors. The enzyme system is inactivated by low pH and activity is restored by the addition of flavin adenine dinucleotide. ring takes place by direct dehydrogenation rather than by hydroxylation followed by dehydration. Investigating the aromatization reaction in a cell-free system, Mitoma, Posner, and Leonard (8) were able to show a conversion of cyclohexanecarboxylic acid to hippuric acid by guinea pig liver mitochondria fortified by glycine and a boiled supernatant. A combination of a-ketoglutaric acid, magnesium sulfate, ethylenediaminetetraacetate, glycine, adenosine triphosphate, and cytochrome c replaced the requirement for boiled supernatant. While addition of coenzyme A to this system was not essential, cyclohexanecarboxyl-CoA was converted efficiently to benzoate by mitochondria in the absence of any cofactors. Aromatization of the CoA ester did not depend on the presence of glycine. The cyclohexanecarboxylic acid analogue of hippuric acid was not aromatized by this system. The present report describes the isolation and the properties of soluble enzymes for the conversion of cyclohexanecarboxylCoA to benzoyl-CoA and discusses some aspects of the mechanism of aromatization.