Interaction of phosphoglycerate kinase with phosphatidylserine liposomes.

The interaction of 3-phosphoglycerate kinase from bovine heart with natural phosphatidylserine (I) and synthetic dipalmitoyl phosphatidylserine (II) in form of liposomes was investigated by measuring fluorescence and activity of the enzyme. The addition of increasing amounts of I resulted in progressive quenching of protein fluorescence with no shift in the emission maximum. In contrast, II did not cause any change in the fluorescence. In the presence of low amounts of I and II (lipid/protein molar ratio 10-40) full enzymatic activity of 3-phosphoglycerate kinase was observed even after 80 min of incubation, whereas without phospholipids the activity considerably decreased. At higher lipid concentrations I strongly inactivated the enzyme and the inactivation by II was only insignificant. It was concluded that the phospholipid membrane protects the enzyme against thermal denaturation, whereas the inactivation is mainly due to phospholipid impurities.