The effects of hydration and divalent cations on lamellar-nonlamellar phase transitions in membranes and total lipid extracts from Acholeplasma laidlawii A-EF22 - a [sup 2] H NMR study.

Autor: Niemi, A. E., Andersson, A.-S., Rilfors, L., Lindblom, G., Arvidson, G.
Předmět:
Zdroj: European Biophysics Journal; 1997, Vol. 26 Issue 6, p485, 9p
Abstrakt: Abstract Acholeplasma laidlawii strain A-EF22 was grown in a medium supplemented with 75 micro M alpha-deuterated palmitic acid (16:0-d2) and 75 micro M alpha-deuterated oleic acid (18:1c-d[sub 2]), or with 150 micro m 18:1c-d[sub 2]. The fatty acids were incorporated into the membrane lipids and [sup 2]H NMR spectra were recorded from intact membranes, total lipid extracts, and the combined glucolipid and neutral lipid fractions of a total lipid extract. The lipids in intact membranes form a bilayer structure up to at least 70 Celsius. The same result was obtained with membranes digested with pronase, which removes a large fraction of the membrane proteins. A reversed hexagonal liquid crystalline (H[sub II]) phase was formed below 70 Celsius by the total lipid extracts hydrated with 20 and 30% (w/w) water; in the presence of 40% (w/w) water only one of the extracts formed an H[sub II] phase below 70 Celsius. The H[sub II] phase was formed at higher temperatures with an increasing water content. However, only a lamellar liquid crystalline (La) phase was formed up to 70 Celsius by the total lipid extracts when the water concentrations were 50% (w/w) or higher. The temperature (T[sub LH]) for the L[sub alpha] to H[sub II] phase transition in the combined glucolipid and neutral lipid fractions was only 2-3 Celsius lower than for the total lipids, and the phospholipids thus have a very modest influence on the T[sub LH] value. Physiologically relevant concentrations of Ca[sup 2+] and Mg[sup 2+] ions did not affect the phase equilibria of total lipid extracts significantly. It is concluded from comparison with published data that the membrane lipids of the cell wall-less bacterium A. laidlawii have a smaller tendency to form reversed nonlamellar phases than the membrane lipids of three bacterial species surrounded by a cell wall. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index