CYANOMET HUMAN HEMOGLOBIN CRYSTALLIZED UNDER PHYSIOLOGICAL CONDITIONSEXHIBITS THE Y-QUATERNARY STRUCTURE

Cyanomet human hemoglobin has been crystallized at a chloride ion conc entration and pH similar to physioloscal conditions. Molecular replace ment calculations definitively show that the hemoglobin subunits are a rranged in the Y quaternary form recently discovered in carbon monoxy hemoglobin Ypsilanti (beta 99 Asp-Tyr), and subsequently observed in c arbon monoxy normal human hemoglobin crystallized at low ionic strengt h and low pH. The structure has been refined at 2.09 Angstrom resoluti on to an R-value of 0.232, and further refinement is currently underwa y. Although the refinement is not yet complete, our results are the fi rst indication that the Y structure may represent an important quatern ary form of liganded hemoglobin under physiological buffer conditions. These results suggest the need for a reexamination of structure-funct ion correlations in the hemoglobin system. (C) 1994 Wiley-Liss, Inc.