Calmodulin-binding proteins of calcium-independent type in rat brain synaptosomal membranes: their localization and properties.

Some properties of calmodulin(CaM)-binding proteins (CaMBPs) of the Ca(2+)-independent type were investigated in the synaptosomal membrane (SM) from rat brain using the [125I]CaM gel overlay method. When SM was prepared in the presence of Ca2+, Ca(2+)-independent CaM binding was decreased, whereas the Ca(2+)-dependent type was not altered. All Ca(2+)-independent-type CaMBPs were membrane-bound and scarcely present in the soluble fractions. When SM was heat-denatured, the 24/22.5-kDa CaMBPs could no longer be detected by [125]CaM binding and a new component with higher molecular mass (greater than 200 kDa) was shown to bind CaM in a Ca(2+)-independent manner. A possible effect of cAMP- and Ca2+/CaM-dependent phosphorylation on CaM binding was also examined.