HB MONTEFIORE (ALPHA-126(H9)ASP-]TYR) - HIGH OXYGEN-AFFINITY AND LOSSOF COOPERATIVITY SECONDARY TO C-TERMINAL DISRUPTION

Hb Montefiore was found, in the heterozygous state, in a Puerto Rican female who had a slightly elevated total Hb level, Structural analysis revealed that Asp-alpha 126 was replaced by Tyr, Hb Montefiore migrat es close to HbF (at pH 8.6) and accounts for 20.3% of the hemolysate. Oxygen binding of red blood cells revealed a 40% decrease in the P-50 (pH 7.4) and a low n value of 1.6 (normal: 2.6), Depletion of red bloo d cell 2,3-DPG did not change the results, Stripped Hb Montefiore at p H 7.2 showed an 8-fold reduction in P-50 (0.6 versus 4.6 mm Hg) and ve ry low cooperativity (n = 1.2 versus 2.9 for the control), Heterotopic effecters, as 2,3-diphosphoglycerate and inositol hexaphosphate had a normal effect and in addition, they increased cooperativity, The chlo ride ion effect and the Bohr effect were moderately reduced, A bezafib rate derivative (L345), known to bind alpha 126, increases the P-50 of HbA by 9-fold, but only by 1.5-fold that of Hb Montefiore. Combining these functional studies with intrinsic fluorescence and Resonance Ram an spectroscopy, we interpret the very low n value and the high oxygen affinity for Hb Montefiore as a result of both a destabilized T state that switches to R upon ligand binding and a deoxy T state that binds ligands with higher affinity than that of deoxy HbA. Hb Montefiore st ill binds ligands cooperatively, but the difference in ligand binding properties of the two quaternary states has been drastically reduced.