Carbon-13 Fourier transform nuclear magnetic resonance studies of fractionated Candida utilis membranes

Abstract

13C Fourier transform nuclear magnetic resonance has been used to study the lipid structure and dynamics of fractionated Candida utilis cell membranes. Measurements of the spin-lattice relaxation times indicate the existence of mobility gradients in the direction of increased mobility from the glycerol backbone toward the terminal methyl group of the fatty acid and toward the choline methyls. The temperature dependence of the relaxation times gives activation energies of approximately 4-6 kcal/mol for the rotations about various carbon-carbon bonds which determine the relaxation rates. In general, comparison with data which have been reported for artificial membrane systems indicates that the contributions of protein-lipid interactions to the T1 gradient are of negligible importance in the yeast membrane system. A dynamical model for the motion about bonds near unsaturated bonds which determined the relaxation of the unsaturated carbons is also proposed. Measurements of chemical shifts with temperature also exhibit a correlation with chain position. On the basis of these data a correlation of deltaE, the energy difference between gauche and anti conformations for gamma carboms, with chain position is inferred. In addition, an estimate of 1.2 kcal/mol can be obtained for deltaE for carbons near the end of the fatty acid chain. This value indicates that intermolecular interactions contribute substantially to deltaE since a value of approximately 0.5 kcal/mol can be ascribed to intramolecular interactions.

NMR Studies of Membrane Structure and Dynamics

“…More recently, biosynthetic labeling techniques have allowed detailed investigations of natural membranes with ~3C and 2H NMR. Activation energies calculated from 13C spinlattice relaxation times obtained for yeast cells indicate that the molecular mobility of the membrane is similar to that of model systems (134). This suggests that the perturbation of the bilayer by protein is relatively small in this system.…”

Biological and model membranes studied by nuclear magnetic resonance of spin one half nuclei

“…In this way one can obtain a detailed mapping of the variation of the motion along the carbon chains (Levine et al 1974;Lee et al 19746). Such 13 C T x measurements have turned out to be a fruitful method for comparing different membrane systems (London, Kollman & Matwiyoff, 1975).…”

“…In a binary mixture of unsaturated dielaidoyl PC and dipalmitoyl PC lipids the glycophorin only gave rise to a broad dipalmitoyl PC 13 C signal indicating an increased rate of exchange of dipalmitoyl PC between the two environments or a preference for the glycophorin for the more mobile dielaidoyl PC. By osmotically shocking yeast cell membranes (London et al 1975) one obtains bilayer aggregates that are small enough to have a correlation time for the overall motion that is so short that a high resolution 13 C spectrum is obtained. As shown in Fig.…”

Two-dimensional 1H/13C heteronuclear chemical shift correlation spectroscopy of lipid bilayers

“…Although nuclear magnetic resonance (NMR) spectroscopy has been used extensively for many years to investigate membrane structure and dynamics, high-resolution spectra of intact bilayers and membranes are a recent observation. Early efforts to record high-resolution NMR spectra were limited to studies of membrane components in organic solvents (Chapman and Morrison, 1966) or sonicated membrane fragments (Chapman et al, 1967;Sears, 1975;London et al, 1975). Whether sonicated bilayers are suitable as a model membrane system has been extensively debated since the observed line narrowing could be artifactual due to the creation of small vesicles with highly curved surfaces (Sheetz and Chan, 1972;Lichtenburg et al, 1975;McKay et al, 1978).…”