Studies on the cold-insoluble fraction of the water-extractable soybean proteins. I. Polymerization of the 11 S component through reactions of sulfhydryl groups to form disulfide bonds

Ultracentrifugal studies of the cold-insoluble fraction of soybean protein show it to consist primarily of a globulin having an s20,w value of about 11 S. The 11 S protein is capable of forming polymers which appear to be dimer, trimer, tetramer, etc., linked by disulfide bonds presumed to be formed by air oxidation of sulfhydryl groups existing at the surface of the 11 S molecule. Depolymerization is effected by mercaptoethanol and a variety of other reagents known to cleave disulfide bonds, and polymerization is prevented by treating the 11 S protein with sulfhydryl-blocking reagents. The possibility of disulfide polymerization occurring with other seed globulins is discussed.