Crystalline activated protein B (chymotrypsin B).

The protein isolated from beef pancreas (1) was recently identified as the zymogen of a proteolytic enzyme and provisionally called protein B (2). In this paper a method of crystallization of the activated enzyme is described. Further properties of this enzyme have been studied, suggesting that the activated protein B belongs to the group of chymotrypsins. The strongest evidence for this conclusion came from the work of Dr. Fruton (3) in which the specificity of the activated protein B toward several synthetic peptides has been investigated. The activity was found to be similar to that of the group of chymotrypsins. In view of our own, and particularly Dr. Fruton’s results, we have proposed the name chymotrypsin B for the active enzyme and chymotrypsinogen B for the unactivated form.