Isolation and Partial Characterization of a Native Serine-Type Protease Inhibitor from Bovine Milk

Purification of a native serine-type protease inhibitor from raw bovine milk resulted in the isolation of an inhibitor tentatively identified as al-antitrypsin. Techniques utilized included ammonium sulfate fractionation followed by metal chelate, hydrophobic interaction, and gel filtration chromatography. Inhibitory activity during the isolation procedure was monitored using benzoyl-DL-arginine-pnitroanilide. Molecular weight range of the isolated inhibitor (56,000 to 64,OOO kDa) was comparable with that of human serum al-antitrypsin (60,000 ma). The pH optima were 6.0 and 7.5. The isolated inhibitor was active against trypsin and elastase, but activity against plasmin was not detectable. The inhibitor was a glycoprotein and formed an SDS staple complex with elastase.