Acetylation of Amino Groups and Its Effect on the Structure of Soybean Glycinin

Purified soybean glycinin (11S globulin) was acetylated at three degrees; low (21-51%), middle (60-81%) and high (90-92%) acetylation in lysine residues. With increasing the acetyl content, the β-structure gradually decreased and the random structure increased resulting in the exposure of tyrosine residue. These were determined from the results of optical rotatory dispersion, intrinsic viscosity, ultraviolet and fluorescence measurement. Gel filtration, ultracentrifugation and gel electrophoresis studies showed drastic conformational changes of highly acetylated 11S (over 90%), in which most of the modified protein (75%) polymerized, and the other dissociated into 3S protein. The close relation between the conformation of acetylated 11S and its emulsifying properties was discussed.