INSECT SEX-PHEROMONE BINDING BY BOVINE BETA-LACTOGLOBULIN

The binding of 24 derivatives of Cydia pomonella sex pheromone (dodecanol framework with no, one, or two conjugated double bonds at different positions of the aliphatic chain) and sodium dodecyl sulfate (SDS) to unmodified, acylated, alkylated, and esterified beta-lactoglobulin (BLG) was studied by fluorescence spectrophotometry. Their apparent dissociation constants were in the range 0.2-0.9 x 10(-6) M (apparent molar ratio ca. 1). Dodecyl acetate and SDS displayed the highest affinity for BLG, when (EE)-6,8-dodecadienyl acetate and (E,E)-7,9-dodecadienyl acetate did not bind to BLG in the applied conditions. The apparent dissociation constants of derivatives unconstrained by conjugated double bonds did not differ. The BLG binding affinity of other studied pheromone derivatives depends on (i) the number of double bonds, (ii) their position in the aliphatic chain, and (iii) their isomerisation (Z or E). Since, neither (E)-3-dodecenyl acetate nor (ZE)-8,10-dodecadienyl acetate nor retinol binding constants changed during their simultaneous binding by BLG, it was concluded that they bind in different binding sites on the BLG molecule. Surprisingly, the chemical modifications that increased the hydrophobicity of BLG prevented its binding of the apolar ligand pheromone molecules.