Kinetic study of CO and O-2 binding to horse heart myoglobin reconstitutedwith synthetic iron chlorin green hemes

Carbon monoxide- and oxygen-binding rates and affinities towards horse hear t 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 protohem e IX (1), these reconstituted green hemes exhibit faster association rates with both carbon monoxide and oxygen and lower affinities with oxygen. Thes e results are significant in explaining the role of natural chlorin green h emes, such as the heme d which is present in the respiratory chain of Esche richia coli and is utilized as a terminal oxidase under limited oxygen supp ly. (C) 2000 Elsevier Science B.V. All rights reserved.