Comparison of trypsin inhibitor from colostrum with other crystalline trypsin inhibitors.

We have recently reported (2) the discovery and crystallization of a stoichiometric trypsin inhibitor from bovine colostrum. Several properties of this inhibitor indicated a close similarity to the two trypsin inhibitors from bovine pancreas, the first crystallized by Kunitz and Northrop (3) and the second crystallized by Kazal, Spicer, and Brahinsky (4). It was of interest to examine the comparative properties of the three inhibitors and, when possible, of their respective complexes with trypsinl in order to determine whether the inhibitors were different chemical species. We have therefore studied the electrophoretic mobilities, inhibitory activities toward trypsin, ultraviolet absorption spectra, and molecular weights of the above compounds.