G.
Monticelli, M. Masserini* e B. Berra
Istituto
di Fisiología Generale e Chimica Biologica e *Dipartimento di Chimica e
Biochimica Medica, Università degli Studi, Via Saldini 50, 20133 Milano, Italy
The thermal properties of biomembranes
examined by dífferential calorimetry mimic the properties of bílayers formed
from their isolated lipids or from synthetic lipids.
In this study we have analyzed, by differential
scanning calorimetry (DSC), the thermal behaviour of lipids extracted from
bovine erythrocyte and of their reconstítuted mixtures.
Membrane lipids were extracted from
blood samples of 11 cows and separated in the three components: cholesterol, phospholipids
and glycolipids.
Phospholipid and glycolipid classes were
determined by thin layer chromatography.
Lipids from erythrocyte membrane of
different animals (at controlled diet), at a given time, were pooled together
at a proportional amount like in the original membranes.
DSC was performed on aqueous buffer
dispersions (pH 7.4) of the average lipid components but, ín some cases, the
sample contained lipids ísolated from one animal.
Average phospholipid sample exhibited
two phase transitions: the first at 24 - 26 °C and the second at about 38 °C.
Some scans of phospholípids from one
animal show only the first transítíon which occurs between 23.1 and 25.4 °C
whereas the second phase transition, when occurring, is at very different
temperatures (32.4 - 38.1 °C).
For all average glycolipid samples one
transition was observed at about 35 °C.
Mixtures of cholesterol and
phospholipids show only one broad transition. In these míxtures the transition
temperature is close to that of the second transition of phospholipid samples.
Some correlations between the transition
temperatures and the amounts of different phospholipids in the samples have
been tested but it seems important to consider the fatty acid composition of
the studied míxtures to account for the different levels of saturated and
unsaturated fatty acids.
Proc. Int. Symp. Thermodyn. Appl. Biol. Syst., S. Margherita Ligure, 1988, p. 87.