Aggregation of bovine IRBP is effectively prevented with reducing agent dithiothreitol (DTT). Aggregation typically occurs above 10 mg/ml even in the presence of detergents such as BOG. (A) S300 size exclusion elution profile showing a main peak of monodispersed bIRBP (asterisk), and leading minor peak representing aggregated bIRBP (arrow). (B) Final ion exchange purification of bIRBP from the major S300 peak. (C) Without DTT, higher oligomeric states form during concentration despite presence of BOG (1, precipitant; 2, supernatant). (D) The presence of 4 mM DTT prevented oligomerization. S, molecular weight standards (170, 130, 100, 72 (orange), 55, 40, 35, 25 kDa); Silver stained SDS-10%PAGE.