Decreased activity of peptide-elongation factors after treatment with cholesterol esterase

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Abstract
Peptide-elongation factors were purified from rat liver and treated with cholesterol esterase and phospholipase A2 immobilized on Sepharose 4B. Binding of L[3H]-phenylalanyl-tRNA to 40S ribosomal subunits was decreased by approximately 70% and to polyribosomes by 30% in the presence of the binding factor incubated with cholesterol esterase. Treatment of this factor with immobilized phospholipase A2 decreased the binding to smaller ribosomal subunits by only about 15%. Poly(U)-dependent phenylalanine polymerization by ribosomal subunits was decreased to approximately 30% of its original value by treatment of both elongation factors with cholesterol esterase. The normal activity of esterase-treated elongation factor in both the binding reaction and peptide-elongation assay was fully recovered by the addition of cholesteryl 14-methylhexadecanoate. Different classes of lipids present in peptide-elongation factor 1 have apparently different functions. Whereas phospholipids are required to maintain the structure of heavy aggregates of this factor, the presence of cholesteryl 14-methylhexadecanoate is obviously necessary for the normal function of peptide-elongation factors.