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, distearoylphosphatidylcholine, distearoylphosphatidylglycerol and distearoylphosphatidylethanolamine were studied by differential scanning calorimetry. The presence of distearoyl- and dipalmitoylphosphatidic acid was found 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 interactions. These interactions were also dependent on the pretreatment of the phosphatidic acid before mixing with the protein. No interaction was found if distearoylphosphatidic acid was added in the gel state. (C) 1997 Elsevier Science Limited.