Nuclear magnetic resonance of hemeprotein crystals. Structure of the heme in Physeter catodon ferrimyoglobin and an analysis of hyperfine shifts.

We report the observation of deuterium Fourier transform NMR spectra (obtained by the quadrupole echo method at 8.5 Tesla, corresponding to a 2H resonance frequency of 55.3 MHz) of [meso-alpha, beta, gamma, delta-2H4], [methyl-1,3-2H6], and [methylene-6,7-b-2H4]heme-labeled aquoferrimyoglobin microcrystals (in approximately 90% saturated (NH4)2SO4 at pH 6.8) from Physeter catodon, using the method of magnetic ordering (Rothgeb, T. M. and Oldfield, E. (1981) J. Biol. Chem. 256, 1432-1446). The results, together with those obtained on suitable diamagnetic derivatives, permit partial determination of the static organization of the heme, and the results obtained are in good agreement with those obtained using x-ray crystallography (Takano, T. (1977( J. Mol. Biol. 110, 537-568). We show that resonances near the paramagnetic iron center are subject to extremely large (approximately 500 ppm) hyperfine shifts, which distort the otherwise symmetric 2H spectra. Temperature dependence studies are required to analyze these shifts, which are an order of magnitude larger than those seen in solution NMR spectroscopy. The overall results suggest that 2H solid state NMR spectroscopy of magnetically ordered paramagnetic protein microcrystals may be a useful method for determination of heme organization in systems that for one reason or another are unsuitable for analysis using x-ray diffraction methods.