Incorporation of C14-amino acids into protein of isolated diaphragms: an effect of insulin independent of glucose entry

The effect of glucose concentration and insulin on protein synthesis was investigated using the isolated rat diaphragm and C14-labeled amino acids. When the donor rat has been well fed, the incorporation of histidine-2-C14, lysine-2-C14, phenylalanine-3-C14, and alanine-1-C14 into muscle protein is uninfluenced by glucose concentration in the medium over the range 0–600 mg %. Insulin leads to an increase in C14-amino acid incorporation into muscle protein in the absence of glucose in the medium. This positive effect of insulin in the absence of added glucose is still observed when the diaphragms are pre-incubated for 2 hours prior to adding insulin. These findings suggest an effect of insulin on protein metabolism independent of its action in promoting glucose entry.