Kinetic Study of CO and O₂ Binding to Horse Heart Myoglobin Reconstituted with Synthetic Iron Chlorin Green Hemes

Carbon monoxide- and oxygen-binding rates and affinities towards horse heart myoglobin reconstituted with synthetic iron chlorin and iron oxo-chlorin green hemes (2-4) were measured by flash photolysis and spectrophotometric titrations. In comparison with native myoglobin containing the red protoheme IX (1), these reconstituted green hemes exhibit faster association rates with both carbon monoxide and oxygen and lower affinities with oxygen. These results are significant in explaining the role of natural chlorin green hemes, such as the heme d which is present in the respiratory chain of Escherichia coli and is utilized as a terminal oxidase under limited oxygen supply.