Transfer Complex of Phospholipid and Cholesterol

Cholesterol is ubiquitous for nearly all mammalian membranes and is generally present in a 1 1 stoichiometry with phospholipids/ The structural and functional roles of cholesterol in biological membranes are not known. Several of the properties of this lipid are anomalous. For instance, it has an extinction coefficient of 20 x 10 with a maximum in the uv absorption at 235 nm.  

Cholesterol reduces the permeability of phospholipid bilayers to solutes such as Na, Cl , and glucose. Introduction of cholesterol into diether phosphatidylcholine membranes does not significantly affect their permeability for It was concluded that the ester carbonyls are 

The importance of phospholipid carbonyls for the transmembrane ion conductance is further exemplified by the observation that the ester carbonyls contribute significantly to the capacitance of phospholipid bilayers with a reciprocal relationship in the 0.1-50-Hz range. The noise spectrum of an axon is dominated by capacitance and is of the/ type in a range covering the above frequencies.  

Upon dissociation of the phospholipid-cholesterol charge-transfer complex the liberated phospholipid molecule should adopt the thermodynamically favorable crystalline state predicted from the discharge of the counterions from phosphatidylserine as well as from the high content of saturated lipids in the nerve membrane. During passage of an action poten- 

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