Hemoglobin Legnano (α2 141 (HC3) Arg→Leu β2) A New High Oxygen Affinity Variant

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Abstract
Hb Legnano (α2 141 (HC3) Arg→Leu β2) is an abnormal hemoglobin, for which preliminary structural and functional studies demonstrated an amino acid substitution (Arg→Leu) in the α-C-terminus. This substitution modifies the functional properties observed in whole blood as well as in red blood cells, as reported in this paper. On the basis of its pI, previously determined by analytical isoelectric focusing (IEF), Hb Legnano was purified on a preparative IEF slab. The purified fraction was subjected to functional ultracentrifugal studies under various conditions of pH and salt concentration. The findings are compared with those for Hb Suresnes (α2 141 (HC3) Arg→His β2) and Hb-CPB, a normal hemoglobin in which the C-terminal α141 Arg has been cleaved by carboxypeptidase B. Hb Legnano, like the other hemoglobins considered, shows an increased P50 a decreased Hill's “n” values and a decreased Bohr effect that are partially restored in presence of organic phosphates. The presence of inorganic ions decreases the Bohr effect and enhances the dissociation into dimers, as observed in Hb-CPB. The dissociation of hemoglobin in carboxy form in ultracentrilugal studies and the different slope of Hill's “n” value as a function of pH are presumably due to presence of Leu, which probably modifies the stereochemistry of the variant.

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