A specific apoprotein activator for lipoprotein lipase

These studies were designed to determine which of the apoproteins of high density lipoprotein (HDL) function as the cofactor for lipoprotein lipase (LPL). ApoLP-gln and apoLP-thr, the major HDL apoproteins, as well as apoLP-val, a minor apoprotein constituent, are inactive as cofactors even in the presence of phospholipid. ApoLP-ala, another minor constituent, is inactive alone but in the presence of phospholipid stimulates lipase activity twofold. Only apoLP-glu is able to stimulate LPL activity in the absence of phospholipid and, in the presence of phospholipid, increases activity twelvefold over baseline levels. It is possible that apoLP-glu and perhaps apoLP-ala are obligatory “co-factors” for the hydrolytic step required for normal clearing of triglyceride from the plasma.