J. Agric. Food Chem. 42 : 2120-2125 (1994)

Functional Changes in Beta-Lactoglobulin by Conjugation with Carboxymethyl Dextran

M. Hattori, K. Nagasawa, A. Ametani, S. Kaminogawa and K. Takahashi

Department ofApplied Biological Science,
Faculty of Agriculture,
Tokyo University of Agriculture and Technology
Tokyo 183, Japan

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