Probing the fatty acid binding site of beta-lactoglobulins

The interactions of fatty acids with porcine and bovine beta-lactoglobulins were measured using tryptophan fluorescence enhancement. In the case of bovine beta-lactoglobulin, the apparent binding constants for most of the saturated and unsaturated fatty acids were in the range of 10(-7) M at neutral pH. Bovine beta-lactoglobulin displays only one high affinity binding site for palmitate with an apparent dissociation constant of 1 x 10(-7) M. The strength of the binding was decreasing in the following way: palmitate > stearate > myristate > arachidonate > laurate. Caprylic and capric acids are not bound at all. The affinity of beta-lactoglobulin for palmitate decreased as the pH of the incubation medium was lowered and BLG/palmitate complex was not observed at pH's lower than 4.5. Surprisingly, chemically modified bovine beta-lactoglobulin and porcine beta-lactoglobulin did not bind fatty acids in the applied conditions.