The aromatization of cyclohexanecarboxyl-CoA to hippuric acid by guinea pig liver mitochondria: submitochondrial localization

Summary The conversion of cyclohexanecarboxyl-CoA to hippuric acid in submit ochondrial fractions from guinea pig liver was studied using a gas chromatographic-mass spectrometric method employing selected ion monitoring. Comparison of the activities of the cyclohexanecarboxyl-CoA to hippuric acid converting system (CCoAHC-system) and marker enzymes in the various submit ochondrial fractions showed that the CCoAHC-system is localized in the mitochondrial matrix. Partial separation of the inner and outer membranes has been accomplished by treating mitochondria with digitonin in isotonic medium and fractionating the treated mitochondria by differential centrifugation. A digitonin-protein ratio of 2.6 mg of digitonin/10 mg of protein must be used in order to release significant amounts of amine oxidase activity (outer membrane marker) from low speed mitochondrial pellets. This pellet still contained most of the glutamate dehydrogenase activity and was insignificantly contaminated with adenylate kinase. Moderate concentrations of phenazine methosulfate (PMS) greatly stimulated the activity of the CCoAHC-system, even in intact mitochondria (optimal concentration of PMS: 1 mM) whilst higher concentrations (> 1 mM) decreased the activity. The formation of hippuric acid in these mitochondrial preparations was linear with time for at least 40 min and linear with respect to protein concentration up to approximately 2.0 mg mitochondrial protein·m¹.