Physiologic Fitness of Enterokinase ∗

Abstract

Summary

For the activation of trypsinogen by enterokinase the optimal concentration of calcium chloride was near 0.0002 M, which is at the lower end of the range of calcium concentrations prevailing in the upper small intestine. Magnesium chloride was not so effective. For an hour's activation at pH 7.7 and 23°, in the presence of 0.0002 M calcium chloride, the rate of trypsin production was directly proportional to the concentration of enterokinase. This system was used for a simplified assay of trypsinogen-activator; and calcium was varied according to whether the activator was enterokinase or trypsin. Although partially purified enterokinase had much more trypsinogen-activating effect than an equal weight of crystallized trypsin, it had much less hydrolytic effect on lysine methylester and tosylarginine methylester. In comparison with trypsin, enterokinase is more precisely adapted to the activation of trypsinogen.