Evidence for Protein Synthesis in Synaptosomal Membranes

Evidence is presented that a brain fraction containing synaptosomal membrane fragments and ghosts prepared from lysed rat forebrain synaptosomes synthesize protein in a cell free system. The protein synthesis was dependent upon the addition of a synaptosomal membrane fraction, Mg++, monovalent cations, ATP, GTP, and enzyme factors prepared from intact synaptosomes. Protein synthesis was inhibited by ribonuclease, cyclohexamide, puromycin, and phosphate ion, but chloramphenicol, erythromycin, ouabain, and KCN had no significant effect. The products of protein synthesis with both the synaptosomal membrane fraction and microsomal fractions from rat forebrain were analyzed by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The distribution of the synaptosomal membrane fraction product in the polyacrylamide gels differed significantly from the microsomal product. Also the distribution of products following density gradient centrifugation and a comparison of requirements for monovalent cations further differentiated protein synthesis with the synaptosomal membrane fraction from that with microsomal preparations.