Benzylamine metabolism at low O2 concentrations. Relative sensitivities of monoamine oxidase, aldehyde dehydrogenase and hippurate synthesis to hypoxia.

The O2 dependence of the metabolism of benzylamine to benzaldehyde, benzoate and hippurate was studied in isolated rat hepatocytes. The initial oxidation to benzaldehyde, catalyzed by monoamine oxidase, had an apparent Kmo2 value of 34 microM in cells and 40 microM in isolated rat liver mitochondria. The conversion of benzaldehyde to benzoate was essentially independent of O2 concentration in spite of the dependence of the reaction upon cytosolic NAD+. The conversion of benzoate to hippurate was half-maximal at 2.4 microM O2 in hepatocytes and at about 0.5 microM O2 in rat liver mitochondria. These values are consistent with the O2 dependence of bioenergetic changes in these preparations and indicate that the O2 dependence of hippurate formation is due to ATP availability for synthesis of benzoyl-CoA. These studies show that the three metabolic processes involved in benzylamine metabolism have markedly different dependences upon O2 and that metabolism of benzylamine by monoamine oxidase is O2 dependent over a physiologically important range.