HB VILLAVERDE [BETA-89 (F5) SER-]THR] - THE STRUCTURAL MODIFICATION OF AN INTRASUBUNIT CONTACT IS RESPONSIBLE FOR A HIGH OXYGEN-AFFINITY

Hb Villaverde [beta 89 (F5) Ser --> Thr], identified in a Spanish pati ent, is a new human hemoglobin variant, electrophoreticaly silent, res ponsible for a severe erythrocytosis. This abnormal hemoglobin display s a very high oxygen affinity and a markedly reduced cooperativity tha t is partly restored in the presence of IHP. Determination of the stru ctural abnormality was achieved on a mixture of the normal and abnorma l beta-chains. After isolation of the abnormal tryptic peptide by RP-H PLC, its sequence was determined by mass spectrometry. The structural abnormality disturbs the intrasubunit interaction between helices F an d H and, thus, may weaken the C-terminal bonds of the deoxy conformati on and the heme contacts of several hydrophobic residues. Hb Villaverd e demonstrates that this intrasubunit contact between helices F and H is essential for the cohesion of the hemoglobin molecule.