CALORIMETRIC STUDIES OF INTERACTIONS BETWEEN BETA-LACTOGLOBULIN AND PHOSPHOLIPIDS IN SOLUTIONS

Interactions between beta-lactoglobulin and phosphatidic acid isolated from egg yolk, distearoyl- and dipalmitoylphosphatidic acid, distearo ylphosphatidylcholine, distearoylphosphatidylglycerol and distearoylph osphatidylethanolamine were studied by differential scanning calorimet ry. The presence of distearoyl- and dipalmitoylphosphatidic acid was f ound to increase the temperature at which thermally induced unfolding of beta-lactoglobulin takes place. However, phosphatidic acid from egg yolk, which has a high proportion of unsaturated acyl chains, did not affect the unfolding temperature. Similarly, no effect on the thermal behaviour of beta-lactoglobulin in the presence of the other classes of distearoylphospholipids was observed. Thus, the acyl chains as well as the polar head group appeared to have an impact on the interaction s. These interactions were also dependent on the pretreatment of the p hosphatidic acid before mixing with the protein. No interaction was fo und if distearoylphosphatidic acid was added in the gel state. (C) 199 7 Elsevier Science Limited.