Effects of Extracellular Proteases on Incorporation of Amino Acids into Protein by Isolated Rat Tissues

With isolated fat cells, trypsin, α-chymotrypsin, and B. subtilis alkaline protease stimulated glucose oxidation and inhibited lipolysis, as did insulin. Only insulin and α-chymotrypsin stimulated incorporation of ³H-leucine into protein. B. thermoproteolyticus thermolysin had no effect on glucose metabolism or lipolysis, but inhibited leucine incorporation. With isolated hemidiaphragms, insulin, trypsin, and α-chymotrypsin stimulated uptake of glucose, but only insulin promoted incorporation of ¹⁴C-methionine into protein. We conclude that the actions of proteases on isolated tissues are not genuinely “insulin-like,” because they do not entail the full spectrum of effects of the hormone.