CA2-ATPASE PUMP FORMS AND AN ENDOGENOUS INHIBITOR IN BOVINE BRAIN SYNAPTOSOMES()

Two forms of Ca2+-pump were identified in bovine brain synaptic membra nes as aspartylphosphate intermediates and were characterized The 140 kDa and 97 kDa phosphoproteins were digested by calpain, producing two phosphorylated fragments, of M.W. 124 and 80 kDa respectively, not in hibited by thapsigargin, and displayed a trypsin digestion pattern wit h the formation of one phosphorylatable fragment of about 80 kDa. Thes e results suggest that both pumps belong to the Plasma Membrane-type o f Ca2+ ATPases, differing from the Sarco- or Endoplasmic Reticulum kin d. A plasma membrane Ca2+-ATPase proteinaceous inhibitor with molecula r weight between 6,000 and 10,000 Da was resolved from synaptic termin al cytosol, where it is enriched by fourfold with respect to frontal c ortex brain cytosol. Such enrichment is already evident in the corresp ondent crude fractions. The presence of calcium pump and its proteinac eous inhibitor inside the synaptic terminals from bovine brain is disc ussed in terms of free calcium level regulation in neuron synaptoplasm .