Skip to main content
ARS Home » Midwest Area » Peoria, Illinois » National Center for Agricultural Utilization Research » Plant Polymer Research » Research » Publications at this Location » Publication #108996
Title: BOWMAN-BIRK INHIBITORS IN SOYBEAN SEED COATS

Author
item Sessa, David
item WOLF, WALTER - BRADLEY UNIVERSITY

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2000
Publication Date: 10/18/2000
Citation: N/A

Interpretive Summary: The U.S. annual production of soybean seed coats (hulls) is over 2 billion pounds at a price of 3 cents/lb. Hulls, for the most part, are used in animal feeds and have some usage as a source of food grade fiber as well as soybean peroxidase which enzyme is used in industry. We isolated and characterized for the first time Bowman-Birk inhibitors (BBIs) in soybean seed coats. BBIs are low molecular weight proteins that are known to possess cancer chemopreventative and also anticarcinogenic properties. BBI concentrates, currently produced from acidic, aqueous extracts of defatted soybean meal, are very low in the chymotrypsin enzyme inhibitor activity known to be essential in the treatment of a variety of cancers in both animals and humans. Since 1992, BBIs from soybeans have achieved Investigational, New Drug status. BBIs from soybean hulls possess significantly higher enzyme inhibitor activity than concentrates produced from soybean meal. Our findings provide a new use of soybean hulls for the generation of value-added products whose production will benefit the farmer and soy processing industry and whose product will benefit all of humanity.

Technical Abstract: Aqueous extracts of soybean seed coats, screened to remove cotyledons, contained peroxidase along with unknown proteins which possessed an estimated molecular weight (MW) of <10 kD when compared with known standards subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). These extracts gave a positive colorimetric assay for trypsin inhibitor (TI) activity. Soybean Bowman-Birk inhibitor (BBI), a known cancer chemopreventative and anticarcinogenic agent, possesses a MW of 8kD. To eliminate the solubilization of peroxidase, we applied the classic methodology of BBI isolation where defatted soybean seed coats were twice extracted with 60% aqueous ethanol to yield a total of 6.96% solids with 1.5% nitrogen and a TI activity of 44mg TI/g solids. The protein components in the 60% ethanol solubles were further concentrated on a CM Sephadex C-25 column eluted with a salt gradient. The econsequent column fractions from the acetone precipitates when subjected t SDS-PAGE yielded a protein which possessed a mobility similar to pure soybean BBI. Since BBI can simultaneously inhibit both trypsin and chymotrypsin, we verified its identification by colormetric assays for TI and chymotrypsin inhibitor (CTI) activities. Chymotrypsin negative stain technique applied to native PAGE of the TI and CTI-active fraction from acetone precipitates showed evidence for eight isoforms of BBI. Based on the summation of CTI active components in the CM Sephadex C-25 column fraction from 60% ethanol extract, its CTI activity relative to CTI in pure BBI is 61.9%. Soybean seed coats may provide a new, inexpensive (6.6 cents/kg) source for BBI concentrate to be used as a potential anticancer agent.