MG2+ CA2+-ATPASE ACTIVITY IS NOT ENRICHED IN SYNAPTIC VESICLES ISOLATED FROM RAT CEREBRAL-CORTEX/

Neuronal ATPases comprise a wide variety of enzymes which are not unif ormly distributed in different membrane preparations. Since purified v esicle fractions have Mg2+/Ca2+-ATPase, the purpose of the present stu dy was to know whether such enzyme activities have a preferential conc entration in a synaptic vesicle fraction in order to be used as marker s for these organelles. Resorting to a procedure developed in this Ins titute, we fractionated the rat cerebral cortex by differential centri fugation following osmotic shock of a crude mitochondrial fraction and separated a purified synaptic vesicle fraction over discontinuous suc rose gradients. Mg2+/Ca2+-ATPase activities and ultrastructural studie s of isolated fractions were carried out. It was observed that similar specific activities for Mg2+/Ca2+-ATPases were found in all fractions studied which contain synaptic vesicles and/or membranes. Although th e present results confirm the presence of Mg2+ and Ca2+-ATPase activit ies in synaptic vesicles preparations, they do not favor the contentio n that Mg2+/Ca2+-ATPase is a good marker for synaptic vesicles.