Cyanomet human hemoglobin crystallized under physiological conditions exhibits the Y quaternary structure

Abstract

Cyanomet human hemoglobin has been crystallized at a chloride ion concentration and pH similar to physiological conditions. Molecular replacement calculations definitively show that the hemoglobin subunits are arranged in the Y quaternary form recently discovered in carbon monoxy hemoglobin Ypsilanti (99 Asp–Tyr), and subsequently observed in carbon monoxy normal human hemoglobin crystallized at low ionic strength and low pH. The structure has been refined at 2.09 Å resolution to an R-value of 0.232, and further refinement is currently underway. Although the refinement is not yet complete, our results are the first indication that the Y structure may represent an important quaternary form of liganded hemoglobin under physiological buffer conditions. These results suggest the need for a reexamination of structure–function correlations in the hemoglobin system. © 1994 John Wiley & Sons, Inc.