Modification of lipoprotein lipase catalytic activity by sialic acids

The role of sialic acid linked with lipoprotein lipase (LPL) in its catalyt ic activity was studied. When LPL was treated with sialidase, the molecular weight decreased by 2000. The sialidase-treated LPL showed unchanged hydro lyzing activity for tributyrin, a water-soluble substrate of esterase, comp ared with the untreated LPL. The sialidase-treated LPL also showed similar hydrolyzing activity for triolein emulsified with Triton X-100, phosphatidy lcholine and phosphatidylethanolamine, whereas it showed significantly incr eased hydrolyzing activity for triolein emulsified with phosphatidylserine and cardiolipin (152% and 183%, compared with untreated LPL, respectively). In addition, the sialidase-treated LPL showed significantly increased hydr olyzing activity against triolein incorporated into very low-density lipopr oteins and chylomicrons (151% and 186% compared with the untreated LPL, res pectively). These results suggest that the loss of sialic acids does not mo dify the function of the catalytic site of LPL, but facilitates the interac tion of the enzyme with the interface of the surface of substrate lipoprote ins.