[Limited proteolysis of brain-specific protein S100. Isolation, physico-chemical and immunochemical characteristics of the neuropeptide AT-1-1].

Six peptides (presumably products of natural protein S100 catabolism) were isolated from bovine brain extracts by hydrophobic chromatography, affinity chromatography on immobilized antiprotein S100 antibodies, gel filtration and chromatography on TSK HW-40 columns in a methanol: water system. At 10(-12) M, peptide AT-I-I caused a 70% inhibition of the specific binding activity of endogenous benzodiazepine brain receptors. When used at higher concentrations (10(-9)-10(-5) M), AT-I-I inhibited the binding activity of central serotonin, dopamine and m-cholinoreceptors. Immunochemical analysis revealed the presence of identical material in rat brain glial cell nuclei (astrocytes). Using a solid phase immunoenzymatic assay, it was shown that peptide AT-I-I was not identical to any other of the 14 peptides tested (commercial preparations). Data from immunochemical analysis testified to the species non-specificity of AT-I-I. It was concluded that in brain tissue natural proteolysis of proteins S100 leads to the formation of biologically active oligopeptide products that are involved, in particular, in the modulation of the functional activity of central benzodiazepine receptors.