BINDING OF CO TO MYOGLOBIN FROM A HEME POCKET DOCKING SITE TO FORM NEARLY LINEAR FE-C-O

The relative orientations of carbon monoxide (CO) bound to and photodi ssociated from myoglobin in solution have been determined with time-re solved infrared polarization spectroscopy. The bound CO is oriented le ss than or equal to 7 degrees from the heme normal, corresponding to n early linear Fe-C-O. Upon dissociation from the Fe, CO becomes trapped in a docking site that orientationally constrains it to lie approxima tely in the plane of the heme. Because the bound and ''docked'' CO are oriented in nearly orthogonal directions, CO binding from the docking site is suppressed. These solution results help to establish how myog lobin discriminates against CO, a controversial issue dominated by the misconception that Fe-C-O is bent.