High pressure NMR studies of hemoproteins. The effect of pressure on the quaternary structure of hemoglobin.

Proton NMR spectra for nitrosyl-, aquomet - and deoxy des-Arg (alpha 141)-hemoglobin in H2O were studied at high pressures up to 1400 atm with attention to the exchangeable proton resonances due to the intra- and intersubunit hydrogen bonds. For aquomethemoglobin , the T state marker signal at 6.4 ppm is insensitive to pressure while the R state marker signal at 6.0 ppm exhibits progressive upfield shift upon pressurization . For nitrosylhemoglobin, the T state signals at 9.6 and 6.5 ppm decrease their intensities upon pressurization while the R state marker signal at 6. 0 ppm remains unchanged. Pressure-induced spectral changes for some of exchangeable resonances are also encountered for deoxy des-Arg (alpha 141)-hemoglobin while the R and T quaternary structural indicators at 6.0 and 9.4 ppm are insensitive to pressure. These pressure-induced spectral changes for these hemoglobin derivatives are significantly distinguished from those associated with the R-T transition induced by addition of IHP or by variation of pH. It is therefore concluded that pressure induces subtle quaternary structural changes in these hemoglobin derivatives without causing the R-T transition.