A comparison of the counteracting effects of glycine betaine and TMAO on the activity of RNase A in aqueous urea solution.
Trimethylamine-N-oxide (TMAO) and glycine betaine are counteracting osmolytes found in cellular systems under osmotic stress, often in association with high urea concentrations. TMAO is a characteristic component of cartilaginous fish and marine molluscs, while glycine betaine is more widely distributed, occurring in plants, bacteria and the mammalian kidney. As part of a project to explain and understand the action of these methylamines, the RNase A-catalysed degradation of polyuridylic acid in the presence of urea and various osmolytes (0-1.0 M) was studied using (31)P Nuclear Magnetic Resonance spectroscopy. The decrease in reaction rate induced by urea could be fully recovered with 1 molar equivalent of trimethylamine-N-oxide or 1.4 molar equivalents of glycine betaine. These results indicate that the modification of RNase A activity induced by urea is not associated with gross irreversible structural changes and that both glycine betaine and trimethylamine-N-oxide have kinetically detectable counteracting effects.
Samuelsson
L M
LM
Department of Physiology, University of Otago Medical School, University of Otago, P.O. Box 913, Dunedin 9001, New Zealand.
Bedford
J J
JJ
Smith
R A J
RA
Leader
J P
JP
D000818:Animals; D001622:Betaine / Q000494:pharmacology*; D002384:Catalysis; D002417:Cattle; D009682:Magnetic Resonance Spectroscopy; D008744:Methylamines / Q000494:pharmacology*; D015394:Molecular Structure; D012313:RNA / Q000737:chemistry / Q000378:metabolism; D012259:Ribonuclease, Pancreatic / Q000378:metabolism*; D012996:Solutions; D014508:Urea / Q000494:pharmacology*
D008744:Methylamines; D012996:Solutions; D001622:Betaine; D012313:RNA; D014508:Urea; D012259:Ribonuclease, Pancreatic; C005855:trimethyloxamine