A 39 kD barley seed protein of the serpin superfamily inhibits alpha-chymotrypsin

A 39 kD protein has been extracted from barley flour with 0.1 M monothioglycerol at pH 5.0 and purified by (NH4)2SO4-precipitation, anion exchange and molecular sieve chromatography. It is an N-terminally blocked, non-glycosylated, single-chain protein present in at least two molecular forms of isoelectric points 5.18 and 5.22. The amino acid composition and partial sequence analysis reveal a relationship to barley endosperm Z protein which belongs to the serpin superfamily. The 39 kD protein inhibits alpha-chymotrypsin while little or no effect could be demonstrated on trypsin, subtilisin, proteinase K, S. aureus V8 protease, thermolysin or two malt thiol endoproteinases. The 39 kD protein is immunochemically related to the major protein component in beer.