bohr effect

In the Bohr effect, protonation of the N-terminal amino groups of of hemoglobin's alpha chains is responsible for 30% of the 0.6 mol of H+ that combine with Hb upon the relaease of 1 mol of O2 at pH 7.4. Assuming that this group has a pKa 7.0 in oxyHb, what is its pKa in deoxyHb?