Lipolysis of ApoC-II deficient very low density lipoproteins: Enhancement of lipoprotein lipase action by synthetic fragments of ApoC-II

Enzymic hydrolysis of triacylglycerol has been studied with very low density lipoproteins from an individual with a genetically determined absence of apoC-II, the activator apoprotein for lipoprotein lipase. Normal rates of ester cleavage by purified bovine milk lipoprotein lipase can be achieved in vitro with native apoC-II and by three shorter synthetic peptides, apoC-II(55-78), apoC-II(50-78) and apoC-II(43-78), which contain part of the carboxyl terminal third of the native apoprotein. At 0.5 μM concentration, all peptides produced a 7-fold activation. ApoC-II(43-78), but not apoC-II(50-78) or apoC-II(55-78), could bind VLDL as shown by separation of unbound ¹²⁵I peptides and the lipoproteins. Thus, residues 43-50 of apoC-II are part of a lipid binding region. High affinity binding of apoC-II peptides to the lipoprotein substrate is not obligatory for activation of lipoprotein lipase.