FUNCTIONAL-CHANGES IN BETA-LACTOGLOBULIN BY CONJUGATION WITH CARBOXYMETHYL DEXTRAN

Two bovine beta-lactoglobulin-carboxymethyl dextran (beta-LG-CMD) conjugates (conjugates 10A and 10B) were prepared to improve the protein function by using water-soluble carbodiimide. The molar ratios of beta-LG to CMD in the conjugates (Conj) were 7:2 (Conj 10A) and 1:1 (Conj 10B). The isoelectric point of each conjugate was 4.7-4.8, which is lower than that of beta-LG. Spectroscopic studies suggested that the conformation around had not changed in either conjugate but the alpha-helix content of Conj 10A had markedly decreased as compared with that of beta-LG. Structural analyses with monoclonal antibodies indicated the conformational change of 125Thr-135Lys (a-helix) in Conj 10A and of 15Val-29Ile (beta-sheet) in Conj 10B. The denaturation temperature of each conjugate was about 89 degrees C, which is much higher than that of native beta-LG, Each conjugate maintained retinol binding activity as strong as that of native beta-LG. The emulsifying activity of beta-LG at neutral pH was much improved by conjugation with CMD.