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

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... t 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.