Cereal Chem 44:653 - 668.  |  VIEW ARTICLE
Cryoprecipitation of Soybean 11S Protein.

W. J. Wolf and D. A. Sly. Copyright 1967 by the American Association of Cereal Chemists, Inc. 

Cooling a concentrated aqueous extract of defatted soybean meal causes cryoprecipitation of protein consisting primarily of the 11S ultracentrifugal component. Factors affecting cryoprecipitation were studied to determine whether this component could be removed quantitatively from a water extract of meal by cooling, to increase the yield of 11S protein and simplify fractionation of 2S and 7S proteins. Factors studied were meal:water extraction ratio, extraction temperature, rate of cryoprecipitation, pH, and addition of mercaptoethanol, NEMI, sucrose, and salts. Extracts (meal:water ratio 1:5) prepared at 40 C. contained more 7S, 11S, and 15S than those prepared at 25 C. and yielded a nearly twofold increase in amount of 11S protein which precipitated when extracts were cooled. Cryoprecipitation was complete or nearly complete in 1-2 hr. Addition of 0.01M mercaptoethanol or NEMI had no effect on amount of cryoprecipitate obtained. Concentrations of NaCl greater than 0.3M and of sucrose greater than 0.6M prevented cryoprecipitation. Addition of CaCl2 to water extract before cooling caused nearly quantitative precipitation of 11S and 15S, plus part of 2S and 7S proteins. Results were similar when water extract pH was lowered from initial 6.3 to 5.2 before cooling. Hydroxylapatite chromatography of 2S and 7S protein mixture remaining soluble at pH 5.4 and 0-2 C. yielded 7S preparations of 83-90% purity. Such samples dimerized nearly completely at pH 7.6, 0.1 ionic strength.