Method for measuring the activities of cholesteryl ester transfer protein (lipid transfer protein)

A continuous recording fluorescence assay was developed for cholesteryl ester transfer protein (CETP). The assay measures the increase in fluorescence accompanying the relocation of fluorescent lipids, cholesteryl esters and triglycerides, from a donor emulsion to an acceptor emulsion. In the absence of CETP, the quantum yields of the fluorescent lipids is low because their high concentrations in the donor emulsions result in self-quenching. CETP catalyzes the redistribution of the fluorescent lipids from the donor to the acceptor emulsions and fluorescence increases substantially. Efficient sonication and incorporation of apolipoproteins from human HDL into the emulsions significantly increased the transfer rates. Under optimal conditions, the redistribution of fluorescent compounds reaches equilibrium within < 30 min and the kinetics of this process are consistent with a simple, first-order reaction pathway. The redistribution kinetics support a mechanism of adsorption --> exchange --> desorption --> diffusion.