CYANOMET HUMAN HEMOGLOBIN CRYSTALLIZED UNDER PHYSIOLOGICAL CONDITIONS EXHIBITS THE Y-QUATERNARY STRUCTURE

Cyanomet human hemoglobin has been crystallized at a chloride ion concentration and pH similar to physioloscal conditions. Molecular replacement calculations definitively show that the hemoglobin subunits are arranged in the Y quaternary form recently discovered in carbon monoxy hemoglobin Ypsilanti (beta 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 Angstrom 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. (C) 1994 Wiley-Liss, Inc.