APStracts 5:0022F, 1998.

Effects of glycine betaine and glycerophosphocholine on thermal stability of ribonuclease. Burg, Maurice B., and Eugenia M. Peters. Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung and Blood Institute, Bethesda, Md 20892

APStracts 5:0022F, 1998.

Effects of glycine betaine and glycerophosphocholine on thermal stability of ribonuclease. Urea in renal medullas is high enough to perturb macromolecules, yet the cells survive and function. The counteracting osmolytes hypothesis holds that methylamines, such as glycine betaine (betaine) and glycerophosphocholine (GPC) in renal medullas, stabilize macromolecules and oppose the effects of urea. Although betaine counteracts effects of urea on macromolecules in vitro and protects renal cells from urea in tissue culture, renal cells accumulate GPC rather than betaine in response to high urea both in vivo and in tissue culture. A proposed explanation is that GPC counteracts urea more effectively than betaine. However, we previously found GPC slightly less effective than betaine in counteracting inhibition of pyruvate kinase activity by urea. To test another macromolecule we now compare GPC and betaine in counteracting reduction of the thermal stability of RNAase A by urea. We find that urea decreases the thermal transition, temperature and that betaine and GPC increase it, counteracting urea approximately equally. Therefore, the preference for GPC in response to high urea presumably has some other basis, such, as a lower metabolic cost of GPC accumulation.

Received 18 April 1997; accepted in final form 15 January 1998.
APS Manuscript Number F133-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 28 January 1998