Oxygen‐Affinity Studies of Avian Hemoglobins

Abstract

The oxygenation of hemoglobin is under the control of the regulatory function of organic phosphates. The one in mammals corresponds to 2,3‐bisphosphoglycerate but in birds and turtles appears to be inositol hexakisphosphate. The latter component decreases the oxygen affinity of the two chicken hemoglobin compounds (the minor and the major) and the lone pigeon hemoglobin component. The Bohr effects have also been determined for the two hemoglobin samples. As has already been observed by electrophoresis and by chromatography, pigeon hemoglobin seems to behave more like that of the major chicken component by disclosing analogous log p50 values, i.e. the partial pressure of oxygen corresponding to a 50% load of the hemoglobin.

Reduction in potency and reversal of left‐shifting activity of BW12C with the major and minor components of chicken hemoglobin

“…These proportions show an obvious correspondence with the amounts of the major and minor hemoglobin components of chicken blood [7] and these were therefore isolated and stripped of phosphate for further study. The effects of BW12C on the oxygen dissociation curves of dilute solutions of chicken major and minor hemoglobins are shown in fig.2a and b, respectively.…”

“…No mutant human hemoglobins containing suitable modifications in the vicinity of the a-chain termini were found but chicken hemoglobins appeared interesting. Chicken erythrocytes contain two main hemoglobin types, chicken major (AII, -75%) and chicken minor (AI, -20%) [7]. The major component has the Pro 77cu groups replaced by serine residues [8] and the minor component in addition has the Val la groups replaced by methionine residues [9].…”

Hemoglobin(βC93A)–Albumin Cluster: Mutation of Cysteine‐β93 to Alanine Allows Moderate Reduction of O2 Affinity by Inositol Hexaphosphate

“…Inositol hexaphosphate (IHP), a powerful allosteric effector, binds to the β cleft of the central cavity of native Hb and stabilizes the tense (T) state quaternary structure . Consequently, the addition of IHP causes a reduction of the O 2 affinity of Hb through a phenomenon known as the IHP effect . The allosteric effector, however, does not lower the O 2 affinities of PEG‐(βC93)Hbs .…”

Tertiary conformational transition in sheep hemoglobins induced by reaction with 5,5´-dithiobis(2-nitrobenzoate) and by binding of inositol hexakisphosphate

“…r⇌t or quaternary R⇌T transitions Heterotropic effector molecules -2,3-bisphosphoglycerate (2,3-BPG), inositol-P 6 and bezafibrate -lower the oxygen affinity of hemoglobin [28][29][30][31][32][33][34][35][36] and the reactivity of the CysF9[93]β sulphydryl group [22]. The interpretation of these results in terms of a shift in the equilibrium between the R and T quaternary states in favor of the T state has been questioned with respect to O 2 binding [32,33,35,36] and the reactivity of CysF9[93]β [14].…”