THE CRYSTAL-STRUCTURES OF TROUT HB-I IN THE DEOXY AND CARBONMONOXY FORMS

We have determined the X-ray crystallographic structure of trout Hb I in both the deoxy and carbonmonoxy forms to resolution limits of 2.3 A ngstrom and 2.5 Angstrom, respectively. The overall fold of the molecu le is highly similar to that of human HbA despite the low level of seq uence identity between these proteins. Trout Hb I is unusual in displa ying almost no pH dependence of oxygen binding affinity, and (at most) very weak interactions with heterotropic effector ligands such as org anic phosphates. Comparison of the two quaternary states of the protei n indicates how such effects are minimised and how the low-affinity T state of the protein is stabilised in the absence of heterotropic inte ractions. (C) 1996 Academic Press Limited