Cereal Chem 46:331 - 343.  |  VIEW ARTICLE
Heat Denaturation of Soybean 11S Protein.

W. J. Wolf and T. Tamura. Copyright 1969 by the American Association of Cereal Chemists, Inc. 

Factors influencing heat denaturation of soybean 11S protein were studied. Effects of time of heating at 100 C. in pH 7.6 solution were determined at different ionic strengths with varying levels of mercaptoethanol. Quantity of precipitate formed and composition of the fraction remaining soluble were determined by ultracentrifugal analysis. Heating at 0.5 ionic strength rapidly converted the 11S protein into a fast sedimenting aggregate and a slow sedimenting fraction of 4S. On continued heating, the soluble aggregate increased in size and precipitated. Heating the 11S protein in 0.01 and 0.5M mercaptoethanol accelerated the precipitation reaction. Lowering the ionic strength from 0.5 to 0.1 and to 0.01 in 0.01M mercaptoethanol accelerated disappearance of the 11S protein and formation of the precipitate. When the 11S protein was heated in 0.5 ionic strength buffer containing 0.01M N-ethylmaleimide, a 3S fraction and a soluble aggregate formed. The aggregate did not precipitate on continued heating. Heating apparently disrupts the quaternary structure of the 11S protein with subsequent separation of the subunits into two distinct fractions. One fraction consists of soluble subunits of 3-4S, which are stable to heating for 30 min. or more. The other fraction of subunits has a pronounced tendency to interact to form a soluble aggregate which, in turn, rapidly converts to an insoluble state on continued heating when sulfhydryl groups are present.