| 摘 要： | Acholeplasma laidlawii strain A-EF22 was grown in a medium supplemented with 75 μm
α-deuterated palmitic acid (16:0-d
2) and 75 μm
α-deuterated oleic acid (18:1c-d
2), or with 150 μm 18:1c-d
2. The fatty acids were incorporated into the membrane lipids and 2H 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 °C. The same result was
obtained with membranes digested with pronase, which removes a large fraction of the membrane proteins. A reversed hexagonal
liquid crystalline (HII) phase was formed below 70 °C 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 HII phase below 70 °C. The HII phase was formed at higher temperatures with an increasing water content. However, only a lamellar liquid crystalline (L
α
) phase was formed up to 70 °C by the total lipid extracts when the water concentrations were 50% (w/w) or higher. The temperature
(T
LH) for the L
α
to HII phase transition in the combined glucolipid and neutral lipid fractions was only 2–3 °C lower than for the total lipids,
and the phospholipids thus have a very modest influence on the T
LH value. Physiologically relevant concentrations of Ca2+ and Mg2+ 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.
Received: 10 March 1997 / Accepted: 4 July 1997
|
