Dansyl phosphatidylethanolamine-labeled very low density lipoproteins. A fluorescent probe for monitoring lipolysis

Abstract

The fluorescent phospholipid dansyl phosphatidylethanolamine (DPE) (dansyl, 5-dimethylaminonaphthalene-1-sulfonyl) was incorporated into very low density lipoproteins (VLDL) to form DPE-VLDL. The addition of milk lipoprotein lipase to DPE-VLDL in the presence of albumin resulted in a greater than 3-fold fluorescence increase and a 20 nm blue shift in the wavelength of the emission maxima of the dansyl fluorophore. The lipoprotein lipase-induced fluorescence changes occurred concomitantly with the release of free fatty acids from VLDL. Lipoprotein lipase did not produce fluorescence changes in DPE incorporated into either low or high density lipoproteins. The rate of fluorescence increase in DPE-VLDL was maximal at 37 degrees C, dependent on the concentration of lipoprotein lipase and VLDL, and followed typical Michaelis-Menten kinetics with a Km of 1.0 for lipoprotein lipase. Both the initial rate and the total fluorescence increase correlated well (r = 0.98 and 0.95) with the release of free fatty acids. We conclude that the lipoprotein lipase-induced fluorescence increases in DPE-VLDL provide an accurate, convenient, and the only noninvasive means of following continuously the lipolysis of human VLDL.