alpha-cyclodextrin extracts diacylglycerol from insect high density lipoproteins

alpha-Cyclodextrins are water-soluble cyclic hexamers of glucose units with hydrophobic cavities capable of solubilizing lipophiles, Incubating alpha- cyclodextrin with high density lipophorin from Manduca sexta or Bombyx mori resulted in a cloudy, turbid solution. Centrifugation separated a pale yel lowish precipitate, Thin-layer chromatography analysis of the lipid extract of the precipitate showed that the major lipid was diacylglycerol, while K Br density gradient analysis of the supernatant demonstrated the presence o f a lipid-depleted very high density lipophorin. Transfer of diacylglycerol from lipophorin to cyclodextrin was specific to cyclodextrin and tvas not observed with beta- or gamma-cyclodextrins. pH had no effect on diacylglyce rol transfer to alpha-cyclodextrin. However, the transfer tvas strongly dep endent on the concentration of alpha-cyclodextrin and temperature. Increasi ng the concentration of alpha-cyclodextrin in the incubation mixture was as sociated with the formation of increasingly higher density lipophorins, Thu s, at 20, 30, and 40 mM alpha-cyclodextrin, the density of B, mori lipophor in increased from 1.107 g/ml to 1.123, 1.148, and 1.181 g/ml, respectively, At concentrations greater than 40 nul, alpha-cyclodextrin had no further e ffect on the density of lipophorin, alpha-Cyclodextrin removed at most 83-8 7% of the diacylglycerol present in Lipophorin, Temperature played an impor tant role in altering the amount of diacylglycerols transferred to alpha-cy clodextrin, At 30 mM alpha-cyclodextrin, the amount of diacylglycerol trans ferred at different temperatures was 50% at 4 degrees C, 41% at 15 degrees C, 20% at 28 degrees C, and less than 3% at 37 degrees C. jlr We propose th at diacylglycerol transfers to alpha-cyclodextrin via an aqueous diffusion pathway and that the driving force for the transfer is the formation of an insoluble alpha-cyclodextrin-diacylglycerol complex.