INFLUENCE OF DOLICHOL ON MICROSOMAL MEMBRANE FUNCTIONS

Microsomal membranes from rat liver were extracted with n-pentane in o rder to remove the lipid products of the mevalonate pathway, dolichol, ubiquinone and cholesterol. Dolichol and cholesterol were subsequentl y reincorporated into these extracted membranes. Electron microscopic examination demonstrated that extraction did not alter the vesicular m embrane structure of the microsomes. The extracted vesicles were perme able to uncharged molecules in the same manner as control microsomes b ut had an increased permeability for charged molecules. Enzyme denatur ation was not observed. The contraction of extracted vesicles was grea tly increased when the incubation medium was supplemented with non-pen etrating compounds such as polyethylene glycol and was much greater th an that of control microsomes. When extracted membranes were reconstit uted with dolichol or cholesterol, the original lower degree of contra ction was reestablished. The effects of dolichol reincorporation on a number of microsomal enzyme activities were investigated and some limi ted changes were observed. These results demonstrate that extraction o f microsomes with n-pentane and subsequent reincorporation of dolichol is an effective approach for investigating the functions of this lipi d. Dolichol and cholesterol both affect microsomal membrane fluidity, but only cholesterol modifies the activities of certain integral micro somal membrane enzymes to a larger extent.