ABSTRACT
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.
