Structure of A 0,A 1 and A 3 conformational substates of carbonmonoxy myoglobin

Abstract

Infrared absorption spectra of carbon monoxide molecule coordinated by the heme iron of carbonmonoxy heme proteins are widely used to study their structure and dynamics. In this paper we use results of X-ray study of carbonmonoxy myoglobin to elucidate the structures of spectroscopically observed conformational substates of this protein. It is shown that A₃ substate corresponds to the structure with water molecule hydrogen bonded to the distal histidine, whereas in the A₁ conformation this molecule is absent. We also show that redistribution of electronic density of the distal histidine and the water molecule as a result of their interaction must be taken into account when predicting their positions in the heme pocket.