Carbon-13 nuclear magnetic resonance spectroscopy of suspensions of chinese hamster ovary cells specifically enriched with (methyl-13C)choline.

Abstract

The mammalian Chinese hamster ovary cell line (CHO) was labeled with (methyl-/sup 13/C)choline. Under the conditions used, approximately 42% of the cellular choline was found to be associated with cellular lipids and the remaining 58% was present in the water-soluble fraction of the cell, primarily as phosphorylcholine. The spin-lattice relaxation time (T/sub 1/) of this pool of phosphorylcholine indicates an intracellular viscosity approximately 1.2 times that of H/sub 2/O. Cells fixed with formaldehyde and washed several times did not exhibit /sup 13/C resonances corresponding to free choline or phosphorylcholine and were sufficiently stable to be studied up to 43/sup 0/C. The T/sub 1/ and line width behavior of the methyl resonance was studied as function of temperature in the fixed cells. The T/sub 1/ data exhibited an Arrhenius dependence with an activation energy of 4.3 kcal/mol, similar to that observed for free choline. The line width does not conform to an Arrhenius law and the values obtained for the CHO cells are similar to those previously reported for sonicated lecithin vesicles and to the value obtained in sonicated lecithin vesicles prepared from the extracted CHO cell lipids. The values are significantly smaller than the values reported for unsonicated lecithin dispersions.more » The data are discussed in terms of a theoretical model involving multiple internal rotations. A measurement of the /sup 13/C-/sup 1/H nuclear Overhauser enhancement for the choline methyl carbons in vesicles prepared from the extracted CHO cell lipids gave a value of 3.0 +- 0.3.« less