ATP binding to human hemoglobin in the presence and absence of magnesium ions investigated with 31P NMR spectroscopy and ultrafiltration.

The addition of 3 mM hemoglobin to 1-10 mM ATP solutions at pH 6.75 resulted in a linear relationship between the change in chemical shift (deltadelta) of the gamma-phosphate of ATP and the percent ATP bound to hemoglobin. The data points obtained with oxyhemoglobin and deoxyhemoglobin fell on the same straight line. In the presence of 3 mM Mg2+, the delta delta decreased curvilinearly as the percent ATP bound was raised. In this case, the percent ATP bound to deoxyhemoglobin was greater than to oxyhemoglobin at the same delta delta value, indicating that the extra ATP binding occurs through groups other than phosphate.