ASSOCIATION-DISSOCIATION PHENOMENA IN GLYCININ

Ultraviolet difference spectra indicated that both tyrosine (287 mμ) and tryptophan (293 mμ) groups are exposed by treatment of glycinin with different concentrations of urea and with acid (pH 2.0). Glycinin solutions (0.34%) when heated at temperatures above 70 ° become increasingly turbid and the protein precipitates at 90 °. Glycinin appears to be stable to heating up to 50 ° and very little change is observed between 50 and 70 °. Heat, acid (pH 2.0), alkali (pH 11.0), and urea treatment cause dissociation of glycinin into subunits and subunit association products as examined by disc electrophoresis. Undissociated glycinin molecules can be detected after heat, acid, and alkali treatment by double gel immunodiffusion and immunoelectrophoresis. Urea (6 m) causes irreversible and complete dissociation of the protein into subunits. The subunits of glycinin, and reduced and carboxymethylated glycinin (RCM-glycinin) are soluble in the solvent system phenol-acetic acid-0.2 m mercaptoethanol, 2:1:1, w/v/v made 5 m in urea (PAMU). Disc electrophoresis using the PAMU solvent separates six major sub-units derived from glycinin, and five major subunits from RCM-glycinin. General considerations from existing data about the structure of glycinin are discussed. © 1969.