Fast flip-flop of cholesterol and fatty acids in membranes: implications for membrane transport proteins.
OBJECTIVE
The rates by which unesterified fatty acids and cholesterol move through and desorb from membranes have been difficult to measure, in part because of the simple structures of these lipids but also because methods have generally not clearly distinguished the two steps of membrane transport. Lack of definitive knowledge has given rise to speculation about the mechanism(s) of membrane 'transport' proteins for fatty acids and cholesterol.


RESULTS
New biophysical and biochemical approaches have provided evidence that fatty acids and cholesterol exhibit rapid diffusion (flip-flop), as fast as milliseconds, across both protein-free phospholipid bilayers and cell membranes. In contrast, desorption of the cholesterol molecule from a membrane surface (hours) is much slower than that of common dietary fatty acids (milliseconds to seconds).


CONCLUSIONS
Knowledge of these properties provides a framework for understanding transport and metabolism of cholesterol and fatty acids and how their putative membrane and intracellular transporters might function.
Hamilton
James A
JA
Department of Biophysics, Boston University School of Medicine, Boston, MA 02118, USA. jhamilt@bu.edu
D000327:Adsorption; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism*; D004058:Diffusion; D005227:Fatty Acids / Q000378:metabolism*; D006207:Half-Life; D006801:Humans; D008051:Lipid Bilayers / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism*
D005227:Fatty Acids; D008051:Lipid Bilayers; D026901:Membrane Transport Proteins; D002784:Cholesterol