Comparative Analysis of Terpenoids in Roots of Ipomoea Species Induced by Inoculation of Ceratocystis fimbriata

A 7S protein in soybean globulins consisted of at least nine polypeptide chains (subunits). Complete dissociation into subunits, having a sedimentation coefficient of 1.1~1.4S and a molecular weight of 22,000~24,000, occurred in the presence of 8m urea and 4m guanidine hydrochloride. However, it was found by sedimentation, ultraviolet spectrophotometry and optical rotatory dispersion that the dissociation with various concentrations of urea accompanied simultaneously with the destruction of the internal structure of the protein. No disulfide bond appeared to participate in the binding between subunits from the results of sedimentation and disc electrophoresis. These results suggested that the subunits were very compactly and complicatedly folded on the formation of the gross structure, and hydrophobic bond with hydrogen bond also participated in the interaction between subunits.

The dissociation was interfered with the increase of ionic strength using sodium chloride, particularly in low concentration of urea. In other words, the gross structure of the 7S protein was stabilized with high ionic strength. This inclination was also recognized in alkali denaturation of the 7S protein.

Almost all tyrosine residues in the 7S protein ionized with a pK value (about 11), so they seemed to exist in the same state and to be burried in the interior of the molecule or to be participated in some combinations.