PURIFICATION AND PARTIAL CHARACTERIZATION OF OAT BRAN GLOBULIN

摘要

Oat bran protein isolate was fractionated into Osborne fractions: albumin, globulin, prolamin, and glutelin. Globulin and glutelin were the major fractions. The oat bran globulin (OBG) fraction was purified by ammonium sulfate [(NH4)(2)SO4, 30-80% saturation] precipitation. Purification was achieved at 50% saturation of (NH4)(2)SO4. Purified globulin was analyzed by gel filtration, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and circular dichroism (CD) to determine molecular size, subunit molecular weights, and secondary strucure, respectively. Disulfide linkage (-S-S-) and sulfhydryl (SH) contents were also estimated. Apparent molecular weight of globulin was similar to 330 kDa. SDS-PAGE showed two broad bands, one in the molecular range between 22 and 31 kDa and the other, between 34 and 42 kDa. CD spectra of OBG in phosphate buffer (0.4 M NaCl, pH 7.6) showed that it conformed to a helical structure of similar to 50%, 43% beta-structure, and a low percentage of turns and random coil. In the presence of urea (8 M), conformation was predominantly random coil (similar to 82%) and resembled that of soy 7S globulin. SH content and -S-S-linkages were estimated as 1.0 and 2.1 mu mol/g of protein, respectively.