Panel A: Overall structure of the hemoglobin tetramer. The iron atoms (Fe, yellow spheres) and His146 side chains (green spheres) are specifically indicated. The angle measures the angle between the two planes containing His146FeFe and His146FeFe, respectively. Panel B: temporal change of (from top to bottom) the C–C distance between His146 and His146, the C–C distance between His143 and His143, C RMSD relative to the 2DN2 X-ray structure, and the angle . The dashed lines (black, orange, red) indicate transition points for the 75, 90, and 120 Å boxes, respectively. Cyan and blue arrows indicate the values of the corresponding observables found for the deoxy T (2DN2) and oxy R (2DN3) states, respectively. Top panel is also given in the main MS.