THE BINDING OF CARBON-MONOXIDE AND NITRIC-OXIDE TO LEGHEMOGLOBIN IN COMPARISON WITH OTHER HEMOGLOBINS

Haemoglobins have the ability to discriminate between oxygen and other diatomic molecules. To further understanding of this process the X-ra y crystal structures of carbonmonoxy and nitrosyl-leghaemoglobin have been determined at 1.8 Angstrom resolution. The ligand geometry is dis cussed in detail and the controversial issue of bent versus linear car bon monoxide binding is addressed. The bond angle of 160 degrees for C O-leghaemoglobin is in conflict with recent spectroscopy results on my oglobin but is consistent with angles obtained for myoglobin X-ray cry stal structures. In contrast to the numerous carbon monoxide studies, very little stereochemical information is available for the nitric oxi de adduct of haemoglobin. This is provided by the X-ray structure of N O-leghaemoglobin, which conforms to expected geometry with an Fe-NO an gle of 147 degrees and a lengthened iron-proximal histidine bond. Thus crystallographic evidence is given for the predicted weakening of thi s bond on the binding of nitric oxide. (C) 1996 Academic Press Limited