Multinuclear (C-13, O-17, Fe-57) NMR studies of carbonmonoxy heme proteinsand synthetic model compounds

C-13, O-17 and Fe-57 NMR spectra of several carbonmonoxy hemoprotein models with varying polar and steric effects of the distal organic superstructure , constraints of the proximal side, and porphyrin ruffling are reported. Bo th heme models and heme proteins obey a similar excellent linear delta(C-13 ) versus nu(C-O) relationship which is primarily due to modulation of pi-ba ck-bonding from the Fe d(pi) to CO pi* orbital by the distal pocket polar i nteractions. The lack of correlation between delta(C-13) and delta(O-17) su ggests that the two probes do not reflect a similar type of electronic and structural perturbation. delta(O-17) is not primarily influenced by the loc al distal field interactions and does not correlate with any single structu ral property of the Fe-C-O unit; however, atropisomerism and deformation of the porphyrin geometry appear to play a significant role. Fe-57 shieldings Vary by nearly 900 ppm among various hemes and an excellent correlation wa s found between delta(Fe-57) and the absolute crystallographic average disp lacement of the meso carbon atoms, \C-m\ relative to the porphyrin core mea n plane. The excellent correlation between iron-57 shieldings and the avera ge shieldings of the meso carbons of the porphyrin skeleton of TPP derivati ves suggests that the two probes reflect a similar type of electronic and s tructural perturbation which is primarily porphyrin ruffling. (C) 2000 Else vier Science Inc. All rights reserved.