AN INFRARED STUDY OF BOUND CARBON MONOXIDE IN HUMAN RED BLOOD CELL ISOLATED HEMOGLOBIN AND HEME CARBONYLS

The binding of carbon monoxide to hemes has been studied by high-resolution infrared spectroscopy. Inductive and resonance effects of substituents both on the porphyrin ring (cis effects) and on pyridine that is coordinated to the iron(II) (trans effects), as well as solvent effects in simple synthetic heme derivatives are reported and compared with the infrared difference spectrum of carbonyl-hemoglobin (HbCO — HbO2) to yield a picture of intramolecular interactions that is consistent with hemoglobin structure. Assignment of the infrared absorption bands (VCO) of HbCO and heme-CO has been confirmed by isotopic substitution with [13C]- or [18O]carbon monoxide. The isotopic data for HbCO appear to be more consistent with Hb-Fe-O≡C (oxygen coordinated to the iron) than with the more conventional structure, Hb-Fe-C≡O (carbon coordinated to the iron), while a structure in which CO is bound parallel to the heme appears unlikely. © 1968, American Chemical Society. All rights reserved.