Inhibition by Zn²⁺ of A-form monoamine oxidase in monkey brain mitochondria

The effects of ZnSO₄ on mitochondrial monoamine oxidase (MAO) activity in monkey brain were compared with those in rat and rabbit, in vitro. After preincubation at 25 °C for 20 min with 1 μM ZnSO₄, MAO-A activity in monkey brain was about 50% using serotonin (5-HT) as a substrate, and the inhibition was proportional to the concentration of ZnSO₄. However, ZnSO₄ had no effect on MAO-B activity in monkey brain using β-phenylethylamine (β-PEA) as a substrate. The inhibition by ZnSO₄ of MAO-A activity was competitive and reversible. CdSO₄ also inhibits MAO-A, but not MAO-B in monkey brain mitochondria. ZnSO₄ did not inhibit either MAO-A or MAO-B activity in rat and rabbit brain mitochondria. These results indicate that the inhibiting action of Zn²⁺ differs depending on animal species. In monkey brain mitochondria, MAO-A was highly sensitive to Zn²⁺ and MAO-B was less sensitive. These results also suggest that Zn²⁺ may regulate the level of catecholamine content in monkey brain.