PROPERTIES OF MG2-ATPASE IN RAT-BRAIN SYNAPTIC PLASMA-MEMBRANES()

In the present study distribution and enzymatic properties of ecto-Mg2 +-ATPase were determined in synaptic plasma membrane (SPM) preparation s isolated from the hippocampus, caudate nucleus and whole brains of f emale rats. Western blot analysis using anti-ecto-Mg2+-ATPase antibody revealed the association of Mg2+-ATPase with SPM prepared from all th e three brain sources, yet the enzyme was most abundant in caudate nuc leus membranes, being 30% and 22% more abundant than in the hippocampa l and whole brain tissue SPM, respectively. The evidence is also prese nted that kinetic properties of the brain Mg2+-ATPase are not under th e control of circulating sex steroids. It was confirmed that the enzym e is activated by millimolar concentrations of Mg2+ and that it cannot be effectively inhibited by known ATPase inhibitors. The most pronoun ced differences in kinetic properties observed were 2.5 fold higher ap parent affinity for ATP and 59% higher specific activity of Mg2+-ATPas e of the caudate nucleus as compared with the enzyme from the hippocam pus. On the other hand, the apparent enzyme affinity for Mg2+ was almo st equal in all SPM preparations tested. Taken together, our results s how that ecto-Mg2+-ATPase is not uniformly distributed and differs in respect to affinity for ATP in rat brain regions, thus indicating its substantial role in the process of signal transduction via controlling the levels of extracellular ATP.