Molecular Stability of he Philly (α2β235 (C1) Tyr → Phe)

Abstract

The molecular stability of [human] Hb Philly (.alpha.2.beta.235(C1)Tyr.fwdarw.Phe) with different ligand states was compared with that of Hb A and Hb S, using mechanical shaking and heat stability tests. The rates of mechanical denaturation of the oxy-forms of these Hb decreased in the order of Hb S, Hb Philly and Hb A, with relative ratios of 9.5:5.6:1.0. Upon oxidation to the met-forms, Hb Philly became mechanically most unstable, with ratios of 13.3:23.0:1.8, respectively. The deoxy-forms of Hb A and Hb S were very stable, while that of Hb Philly was as unstable as the oxy-form. The addition of inositol hexaphosphate (IHP) to deoxy-Hb Philly stabilized the molecules. Since IHP restores the cooperative O2 binding of Hb Philly, deoxy-Hb Philly appears to combine with IHP to change the quaternary structure required for cooperative O2 binding and for stabilization of the molecule. Heat stability tests on Hb Philly showed that the oxy- and met-forms were slightly more unstable than those of Hb A, while the deoxy- and carbonmonoxy-forms were as stable as those of Hb A. Results for heat stability tests showed that Hb molecules are stabilized when converted to the deoxy- or carbonmonoxy-forms so that oxidation of Hb into the met-forms is prevented. The stability of Hb apparently depends highly on its ligand state, and the stability of various ligand forms should be tested when Hb stability is investigated.