Extramitochondrial Protein Synthesis in Calf Brain Synaptosomes

Abstract

Isolated synaptosomes of calf brain cortex incorporated labelled amino acids into their mitochondrial, membranous and soluble proteins in an approximate ratio of 1:1:0.5. Synaptosomal protein synthesis was sensitive to ATP, noradrenaline, cycloheximide and puromycin, and together with mitochondrial protein synthesis, also to chloramphenicol, 2.4-dinitrophenol, KCN and hyperosmotic conditions. The absence of Na⁺ and K⁺ ions slightly inhibited both synaptosomal and mitochondrial protein synthesis. Using incorporated radioactivity as an indicator of synthesized proteins, the synaptosomal soluble proteins could be obtained in one large peak in gel filtration on Sephadex G-100 and G-25, and in two components in disc electrophoresis on a 7% polyacrylamide gel. An approximate molecular weight was calculated for the synthesized proteins using known proteins as standards, giving 15000-35000 in the gel filtration eluant, and 27000 and 36000 in the disc electrophoresis bands.