Wray S, Wilkie D R
Department of Physiology, Liverpool University.
J Exp Biol. 1995 Feb;198(Pt 2):373-8. doi: 10.1242/jeb.198.2.373.
Urea is known to be disruptive to proteins, yet high levels occur in a variety of tissues. It has been suggested that trimethylamines counteract the effects of urea on protein. We have, therefore, directly investigated whether elevating tissue urea levels produces an increase in trimethylamine concentrations by using 31P and 14N nuclear magnetic resonance (NMR) spectroscopy to detect two trimethylamines (glycine betaine and glycerylphosphorylcholine) in intact, living gastrocnemius muscle from Xenopus laevis. Xenopus laevis naturally elevates its tissue urea levels under dry conditions. This ability was used to obtain plasma urea levels ranging from 1 to 110 mmol l-1. This procedure did not alter pH or levels of ATP or phosphocreatine in the muscles, but did raise trimethylamine levels. We find that there is a significant relationship between plasma urea concentrations and the trimethylamine levels studied. This relationship was, however, limited to the lower range of urea levels. We propose that other trimethylamines or mechanisms come into play at urea concentrations above 20 mmol l-1.
已知尿素会破坏蛋白质，但在多种组织中都存在高浓度的尿素。有人提出三甲胺可以抵消尿素对蛋白质的影响。因此，我们通过使用31P和14N核磁共振（NMR）光谱法来检测非洲爪蟾完整活腓肠肌中的两种三甲胺（甘氨酸甜菜碱和甘油磷酸胆碱），直接研究了提高组织尿素水平是否会导致三甲胺浓度升高。非洲爪蟾在干燥条件下会自然提高其组织尿素水平。利用这种能力可使血浆尿素水平在1至110 mmol l-1范围内变化。该过程并未改变肌肉的pH值或ATP或磷酸肌酸水平，但确实提高了三甲胺水平。我们发现血浆尿素浓度与所研究的三甲胺水平之间存在显著关系。然而，这种关系仅限于较低的尿素水平范围。我们提出，在尿素浓度高于20 mmol l-1时，其他三甲胺或机制会发挥作用。
