Proteolytic activity of bovine lactoferrin.

Bovine lactoferrin catalyzes the hydrolysis of synthetic substrates (i.e., Z-aminoacyl-7-amido-4-methylcoumarin).
Values of Km and kcat for the bovine lactoferrin catalyzed hydrolysis of Z-Phe-Arg-7-amido-4-methylcoumarin
are 50 ?M and 0.03 s-1, respectively, the optimum pH value is 7.5 at 25 oC. The bovine lactoferrin substrate
specificity is similar to that of trypsin, while the hydrolysis rate is several orders of magnitude lower than that
of trypsin. The bovine lactoferrin catalytic activity is irreversibly inhibited by the serine-protease inhibitors PMSF
and Pefabloc. Moreover, both iron-saturation of the protein and LPS addition strongly inhibit the bovine lactoferrin
activity. Interestingly, bovine lactoferrin undergoes partial auto-proteolytic cleavage at positions Arg415-Lys 416
and Lys440-Lys441. pKa shift calculations indicate that several Ser residues of bovine lactoferrin display the high
nucleophilicity required to potentially catalyze substrate cleavage. However, a definitive identification of the active
site awaits further studies.