Cholesterol behavior in human serum lipoproteins.

A derivative of ergosterol, ergosta-5,7,9,22-tetraen-3 beta-ol, was synthesized and characterized. Its properties in membranes are similar to those of cholesterol as measured by glucose-permeability and by order parameters derived from electron spin resonance of spin-labels. Thus, because of the three conjugated double bonds, this molecule can be used as an optical probe of sterol behavior in membranes. Circular dichroism (CD) spectra of sonicated egg phosphatidylcholine vesicles containing the probe exhibited CD transitions whose intensity was dependent on sterol content. CD spectra from this probe in human low-density and high-density lipoproteins indicated distinctly different environments for the sterol in the two lipoproteins.