Metastable Photoproducts from Carbon Monoxy Myoglobin and Hemoglobin

Abstract

The photodissociation of carbon monoxy hemoglobin and myoglobin has been studies by low temperature resonance Raman scattering to determine the relaxation processes of the photoproducts. In myoglobin the photoproduct generated at very low temperatures (1.6 and 4.2°K) has an expanded heme core when compared to the deoxy preparation. No other differences were found. At higher temperatures the heme relaxes to take on its deoxy conformation. In the hemoglobin photoproduct, over a wide temperature range many vibrational modes have frequencies which differ from their values in deoxy hemoglobin. The differences in behavior between hemoglobin and myoglobin account for the differences in their biological function. In hemoglobin the state of ligand binding is communicated to the protein through interactions between the heme and the surrounding amino acids thereby triggering the cooperative transition. Myoglobin is noncooperative so the heme-protein interactions seen in hemoglobin are absent.