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

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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.

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