Association tendency of beta-lactoglobulin AB purified by gel permeation chromatography as determined by dynamic Light scattering under quiescent conditions

Association properties of beta-lactoglobulin AB (beta-Lg) fractionated by gel permeation chromatography (GPC) was studied using dynamic light scattering (DLS) at a concentration of 5% w/v and pH 7.0 from 25 to 70 degrees C. beta-Lg fraction with a molecular weight of 18.4 kDa by GPC (monomeric) showed self-association at 25 degrees C. At 25 degrees C similar to 58% of the protein had an apparent mean diameter < 10 nm and the rest between 10 and 100 nm. On heating to 35 degrees C all the protein existed as monomers and dimers. With further heating association increased; large particles with an apparent size of 100-599 nm were seen > 45 degrees C indicating that some degree of denaturation occurs even at 45 degrees C. The amount of aggregate < 10 nm in size decreased sharply > 65 degrees C. Data indicate that beta-Lg that was monomeric during GPC, where a linear velocity gradient may exist, was associated even at 25 degrees C under quiescent conditions of the DLS experiments. Association increased progressively with temperature and denaturation, as observed by the formation of large aggregation, starting at 45 degrees C.