Functional protection of human haemoglobin against protein dissociation

The spectroscopic and functional properties of human adult haemoglobin are clearly disrupted by concentrations of urea > 0.4 M. This disruption of structure and function is completely obviated by the presence of 0.2 M trimethylamine N-oxide (TMAO). Spectroscopic data suggest that TMAO prevents urea-induced production of high-spin haem. Functional analysis shows that TMAO exerts its influence by counteracting urea-induced destabilisation of the T state of the haemoglobin protein. Further studies show, however, that TMAO is not able to exert any such stabilising influences in the presence of high concentrations of typical organic solvent denaturants.