Metmyoglobin, conformation

The NO dissociation rate constants are summarized in Table HI (50) and are smaller than those seen with NO-metmyoglobin complexes. NP2 and NP3 (A ofr 0.1 s ) release NO approximately 10 times more slowly than NPl and NP4 kofs 2-3 s ) at pH 8.0, and the NO release rate for all nitrophorins decreases as the pH is lowered to 5.0. The NO release curves cannot be fit with a single exponential, indicating two off rates at each pH, as previously noted for both recombinant and insect-derived NPl (46), and which has also been recently reported for recombinant NP2 (145). The biphasic kinetics suggest the presence of slowly interconverting conformations. The values obtained are pH and protein dependent, ranging from 2.6 to 0.05 (Table HI) (50), values that are considerably slower than found for sperm whale metmyoglobin... 

Fig. 25. Stereodrawings of the two conformations of arginine-45 of carbon monoxy-myoglobin from sperm whale, (a) Conformation I, which is comparable to the conformation normally observed in metmyoglobin from sperm whale, (b) Conformation 2, which is stabilized by an amino-aromatic interaction between arginine-45 and phenylalanine-43.

Parak and collaborators (Hartmann et al., 1987 Parak et al., 1987) carried out X-ray structure analyses for metmyoglobin at temperatures of 80—300 K. One hundred sixty water molecules, more than one-third of the water in the crystals, were included in the refinement. The disorder is higher for water that for protein atoms (Fig. 31). Reduction in temperature partially freezes out the disorder for the water, as for the protein. The residual disorder at low temperature has been understood to represent conformational substates or a distribution of conformations, frozen in at low temperature and in mobile equilibrium at high temperature. 

Conformation of methemoglobin, metmyoglobin, cytochrome c, together with poly-L-lysine and glycogen phosphorylase adsorbed at the mercury electrode, was studied by various polarographic techniques in... 

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