Relationship between enzymatic modifications of serum low density lipoproteins and their haemagglutination inhibiting activity towards Sindbis virus

The chemical structure of human serum low density lipoproteins (LDL) involved in the inhibition of the haemagglutination by Sindbis virus was studied. Separation of lipoproteins into their protein and lipid components demonstrated that the inhibiting activity is almost completely due to the lipid moiety. The treatment of LDL and extracted lipoprotein lipids by phospholipase A2, C and D produced different effects and in particular a marked increase in the HI titre by the action of phospholipase A2. Moreover treatment with glycosidases significantly reduced the HI titre of LDL, thus suggesting the importance of carbohydrate moiety in the inhibiting lipoprotein molecule.