Anabolic Responses of Diaphragm Muscle to Insulin and to Other Pancreatic Proteins.

Several pancreatic hydrolases, when applied to rat diaphragm in the same concentration as 0.5 U/ml beef insulin, actually behaved like the hormone. One-hour cellular uptake of D-xylose was enhanced by insulin, chymotrypsin, and trypsin. Uptake of 3-0-methyl glucose was enhanced by insulin, chymotrypsin, and ribonuclease. Accumulation of L-proline, occurring simultaneously with that of sugar, was selectively increased by trypsin or chymotrypsin. DFP-inactivated chymotrypsin was half as effective as the active enzyme in stimulating pro-line accumulation. Glycogen contents of diaphragms incubated for one hour in 5 mg/ml glucose were increased by trypsin to the same extent as by insulin, and to a lesser extent by carboxypeptidases A and B, elastase, chymotrypsin, and pepsin. Ten-minute incubations in 2.8 mg/ml glucose with insulin or trypsin led to increased glycogen synthesis, while incubation with diiospropylfluorophosphate-inactivated trypsin did not. Attention is focused on the active serine residue of chymotrypsin and trypsin as essential to maximal expression of insulin-like activity of these proteins.