JBC, Vol. 252, Issue 9, 2929-2933, May, 1977
Calorimetric study of microsomal membrane
S. Mabrey, G. Powis, J. B. Schenkman and T. R. Tritton
Differential scanning calorimetric measurements of normal rat liver
microsomes reveal a single thermal transition at about 50 degrees. This
transition is assigned to irreversible prorein denaturation. There is no
evidence for a reversible lipid phase transition at any temperature above 0
degrees, indicating that the microsomal membrane is in teh fluid state
under these conditions. Rats fed a fat-free diet which increases the degree
of saturation of fatty acids in the membrane lipids do produce microsomal
membranes exhibiting a reversible lipid phase transition. The
NADH=dependent and NADPH-dependent enzymatic reductions of cytochrome c
show linear Arrhenius behavior in the normal rat liver microsomes but
reveal discontinuities and breaks in the Arrhenius plots at approximately
the calorimetrically determined phase transition temperatures in microsomes
from rats fed the fat-free diet. Hence, the fluidity of cell membranes can
be altered by diet with consequent effects on membrane-supported functions.
The data further show that the lipid organization of the membrane is not
independent of the protein component and supports models of membrane
structure where a separate class of lipids forms a boundary between the
bulk phase and the proteins.
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