Chlorphentermine inhibits pulmonary mitochondrial monoamine oxidase

Oxidation of six amine substrates by rat, rabbit and guinea-pig lung mitochondrial monoamine oxidase (MAO) was investigated polarographically with a Clark oxygen electrode in the presence of chlorphentermine (CP). This amphiphilic drug decreased the deamination of serotonin, norepinephrine, tyramine and dopamine significantly in all three species. However, the oxidation of tryptamine and benzylamine was unchanged. Amine oxidation by MAO in guinea-pig lung mitochondria was much more sensitive to the CP-mediated inhibition than rat or rabbit. A kinetic study of serotonin oxidation in the absence and presence of CP showed that both Vmax and Km were affected. These combined data indicate that CP is a specific inhibitor of pulmonary, mitochondrial monoamine oxidase form A with mixed-type inhibition.