Calcium disodium edetate enhances type A monoamine oxidase activity in monkey brain.

The effects of metal chelators on monoamine oxidase (MAO) isozymes, MAO-A and MAO-B, in monkey brain mitochondria were investigated in vitro. MAO-A activity increased to about 40% with 0.1 microM calcium disodium edetate (CaNa2EDTA) using serotonin as a substrate, and this activation was proportional to the concentration of CaNa2EDTA. On the other hand, MAO-A activities were decreased gradually with an increasing concentration of o-phenanthroline and diethyldithiocarbamic acid, but these metal chelators had no effect on MAO-B activity in monkey brain. The activation of MAO-A activity by CaNa2EDTA was reversible. CaNa2EDTA did not activate both MAO-A and MAO-B activities in rat brain mitochondria. Zn and Fe ions were found in the mitochondria of monkey brain. Zn ions potently inhibited MAO-A activity, but Fe ions did not inhibit either MAO-A or MAO-B activity in monkey brain mitochondria. These results indicate that the activating action of CaNa2EDTA on MAO-A was the result of the chelating of Zn ions contained in mitochondria by CaNa2EDTA. These results also indicate the possibility that Zn ions may regulate physiologically the level of serotonin and norepinephrine content in brain by inhibiting a MAO-A activity.