Abstract
We have studied the binding of inositol pentaphosphate (IPP) to the hemoglobins from two species of goose living at low and high altitudes, using the proton absorption method. Measurements were done at 25 and 37 degrees C in a pH range between 6.0 and 8.8. The bird hemoglobins show a high affinity and a binding stoichiometry of 1 IPP molecule/hemoglobin tetramer both in the ligated and unligated state, indicating the same binding site for IPP in oxy- and deoxyhemoglobin. The results indicate that the interaction of IPP with both geese hemoglobins is very similar. For the deoxyhemoglobins of both species the IPP-binding constant shows a strong pH dependence extending over a wide pH range (i.e. +/- 2 x 10(6) M at pH 8.8 and +/- 6 x 10(10) M at pH 6.0). The binding constant of IPP for the oxyhemoglobins shows a much weaker pH dependence (i.e. +/- 4 x 10(4) M at pH 8.8 and +/- 3 x 10(6) M at pH 6.0), indicating that the interaction of IPP with the goose hemoglobin is strongly dependent on the state of ligation of the protein. The IPP binding constants for the oxy- and deoxyhemoglobins are found to be in good agreement with the IPP-induced change in oxygen affinity of both hemoglobins as estimated from oxygen binding curves.
Highlights
We have studied the binding of inositol pentaphosphate (IPP) to the hemoglobins from two species of goose living at low and high altitudes, using the proton absorption method
The results indicate that the interaction of IPP with both geese hemoglobins is very similar
For the deoxyhemoglobins of both species the IPP-binding constant shows a strong pH dependence extending over a wide pH range (i.e. +2 x lo6 M at pH 8.8 and 26 X 10” M at pH 6.0)
Summary
We have studied the binding of inositol pentaphosphate (IPP) to the hemoglobins from two species of goose living at low and high altitudes, using the proton absorption method. It has been long known that the blood oxygen affinity of animals residing at high altitude is in general higher than that of lowland species of similar size [1] This pattern was observed in amphibians, mammals, and some birds (l-3). Avian hemoglobins are interesting with respect to their interaction with organic phosphates because they possess a relatively high number of positively charged residues at the phosphate binding site as compared to human hemoglobin [8,9,10] This leads to a very high affinity for in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Organic phosphates even in the oxygenated state [11] which makes it possible to study the interaction of inositol pentaphosphate with the protein over a wide pH range Such measurements provide information on the stoichiometry of the effector binding to oxyhemoglobin and on the nature of the groups interacting with the phosphate
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