The reaction of hemoglobin Zürich with oxygen and carbon monoxide

The present paper reports a spectroscopic and kinetic study of the reaction with oxygen and carbon monoxide of (a) the abnormal hemoglobin Zürich (beta 63, E7 His leads to Arg), (b) its isolated abnormal chains (beta ZH), and (c) a reconstituted hybrid containing cobalt instead of iron on the normal alpha chains (Co alpha)2-(Fe beta ZH)2. The abnormal beta ZH chains, isolated from hemoglobin Zürich (HbZH) tetramer, display very peculiar spectral properties in the Soret region which were determined, for the oxy and deoxy derivatives, by kinetic difference spectra. The spectral properties of abnormal chains are maintained in the native and reconstituted hybrid tetramer. The rate constants for CO and O2 binding to isolated beta ZH chains were compared with those of the normal alpha and beta chains, It is confirmed that the CO combination rate constant to beta ZH is much higher than that of normal chains, whereas that for O2 is similar for the normal and abnormal chains. The CO binding rate constant for Fe beta ZH chains in the hybrid tetramer is the same as in the native HbZH molecule, i.e. much higher than that of normal chain. The new data are fully consistent with the sequential mechanism for CO binding previously proposed by us; on the other hand, on the basis of the spectral and kinetic results, and contrary to what has been suggested by other authors, a sequential binding of the ligand is excluded in the case of O2.