Modification of lipoprotein lipase catalytic activity by sialic acids

The role of sialic acid linked with lipoprotein lipase (LPL) in its catalytic activity was studied. When LPL was treated with sialidase, the molecular weight decreased by 2000. The sialidase-treated LPL showed unchanged hydrolyzing activity for tributyrin, a water-soluble substrate of esterase, compared with the untreated LPL. The sialidase-treated LPL also showed similar hydrolyzing activity for triolein emulsified with Triton X-100, phosphatidylcholine and phosphatidylethanolamine, whereas it showed significantly increased 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 hydrolyzing activity against triolein incorporated into very low-density lipoproteins and chylomicrons (151% and 186%, compared with the untreated LPL, respectively). These results suggest that the loss of sialic acids does not modify the function of the catalytic site of LPL, but facilitates the interaction of the enzyme with the interface of the surface of substrate lipoproteins.