title: The mechanism of activation of lipoprotein lipase by apolipoprotein C-II. The formation of a protein-protein complex in free solution and at a triacylglycerol/water interface.
abstract: The binding of lipoprotein lipase to a fluorescently labelled apolipoprotein C-II in free solution has been followed by measuring fluorescence anisotropy. The formation of a weak, binary complex in which a single apolipoprotein C-II molecule associates non-cooperatively with each subunit of the dimeric enzyme was observed. The dissociation constant for this complex in 0.05 M NaCl is 0.2 X 10(-6) M and it is weakened markedly by raising the salt concentration and by the binding of heparin to the enzyme. The assembly of the same protein-protein complex on the surface of glycerol trioleate globules has been monitored by steady-state and pre-steady-state kinetics. In these circumstances the lipoprotein lipase-apolipoprotein C-II interaction is much tighter (Kd = (7-10) X 10(-9) M) and is insensitive to salt and heparin. The mechanism of activation of the enzyme at low concentrations of apolipoprotein C-II is described by a kinetic model in which apolipoprotein C-II binds preferentially to the form of the enzyme which is associated with the triacylglycerol substrate. This preference leads to a stabilization of the enzyme-substrate complex, thus reducing the apparent Ks.
mesh_terms: D053304:Apolipoprotein C-II; D001056:Apolipoproteins C / Q000494:pharmacology*; D004789:Enzyme Activation; D005454:Fluorescence Polarization; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D008071:Lipoprotein Lipase / Q000378:metabolism*; D008433:Mathematics; D009994:Osmolar Concentration; D012996:Solutions; D014280:Triglycerides; D014867:Water
chemical_list: D053304:Apolipoprotein C-II; D001056:Apolipoproteins C; D012996:Solutions; D014280:Triglycerides; D014867:Water; D006493:Heparin; D008071:Lipoprotein Lipase