Procaine HCl (Gerovital H3): a weak, reversible, fully competitive inhibitor of monoamine oxidase

A specially stabilized form of procaine hydrochloride (Gerovital H3) has been shown to be a more potent inhibitor of monoamine oxidase than procaine HCl itself and a weaker inhibitor of this enzyme than iproniazid. This preparation was studied to determine its mode of interaction with monoamine oxidase using purified rat brain mitochondrial monoamine oxidase as the enzyme source. Reaction velocities were determined spectrophotometrically by quantitating the rate of appearance of 4-hydroxyquinoline from kynuramine. Dilutional studies comparing the mechanism of inhibition of monoamine oxidase produced by Gerovital H3 and by ipronizid demonstrated that Gerovital H3 was a reversible inhibitor of monoamine oxidase. Analysis of studies using Lineweaver-Burk and Dixon plots revealed that Gerovital H3 was a fully competitive inhibitor of monoamine oxidase. That Gerovital H3 is a weak, reversible, competitive inhibitor of monoamine oxidase may explain the absence of adverse reactions associated with the clinical use of Gerovital H3 as compared to the severe adverse reactions that have been associated with the use of irreversible monoamine oxidase inhibitors.