Inhibition of superoxide production in human neutrophils by purified soybean polypeptides. Re-evaluation of the involvement of proteases.

Inhibition of neutrophil superoxide production has been previously reported for reagents and polypeptides which also inhibit serine proteases. There are disagreements between the results of different laboratories including our own, which have attempted to use the Kunitz soybean trypsin inhibitor to block neutrophil superoxide production. Having confirmed that crude extracts of soybean do contain inhibitory factors which affect neutrophil superoxide production, we have resolved polypeptides in an ethanolic extract of soybean flour by anion and cation exchange chromatography and preparative polyacrylamide gel electrophoresis. Fractions have been assayed for protease inhibitory activity and inhibition of neutrophil superoxide production. We have found an inverse relation between these two inhibitory activities during the purification process. Two of three isolated polypeptides are potent inhibitors of neutrophil superoxide production (50% inhibition at 10(-7) M) but retain only weak anti-trypsin activity. A third polypeptide is a potent inhibitor of trypsin but is completely lacking superoxide inhibitory activity. None of the isolated polypeptides inhibit chymotrypsin. The implications of these findings for the hypothetical association between neutrophil production of superoxide and cellular proteases are discussed.