Rat skeletal-muscle elongation factor 2 was assayed by causing it to react with NAD+ by using fragment A of diphtheria toxin as the catalyst. Dietary protein restriction decreased the concentration of elongation factor 2 in homogenates of whole muscle. These decreases paralleled a decline in muscle RNA so that the number of molecules of elongation factor 2 per ribosome appeared to be independent of the diet. We conclude that elongation factor 2 is probably not the factor limiting the rate of muscle protein synthesis and is not responsible for the fall in the protein-synthetic rate in vivo observed in the muscles of animals whose dietary protein intake is inadequate.
