Ultrastructural demonstration of Mg-ATPase activity of the chromaffin granule

Histochemical evidence for magnesium-activated-ATPase activity of chromaffin granules in the hamster adrenal medulla is presented. A modified Wachstein-Meisel medium, using 40 mM magnesium, was employed. Not all chromaffin granules were reactive, but the reaction product was more noticable on noradrenaline granules than adrenaline granules. Presumtive exocytotic sites were very reactive. Small vesicles, elongated-granules, lysosomes, the plasma membrane, the endoplasmic reticulum, and mitochondria were also reactive.