Hb Howick [beta 37(C3)Trp-->Gly]: a new high oxygen affinity variant of the alpha 1 beta 2 contact

Hb Howick or beta 37(C3) Trp-->Gly is a newly described hemoglobin variant found in an adult male. Hematological data and stability by the isopropanol stability test were normal. The abnormal variant comprised 29% of total hemoglobin and migrated in the Hb D position on cellulose acetate at pH 8.6, and in the Hb F position on citrate agar (pH 6.0). Oxygen dissociation studies on the whole blood showed the variant to have a higher oxygen affinity than normal, with a P50 of 19.8 mm Hg (normal, 26 mm Hg). There were also significant differences in the saturation curve. The variant showed a reduced Bohr effect which was manifested as very high oxygen affinity at low pH and saturation. The beta 37 residue is an alpha 1 beta 2 contact site and the substitution of the tryptophan for a glycine would be expected to result in a destabilization of the deoxy-hemoglobin form because of the reduced number of hydrogen bonds, salt bridges and van der Waal contacts between the alpha 1 and beta 2 chains.