Structure of deoxyhemoglobin Cowtown [His HC3(146) beta----Leu]: origin of the alkaline Bohr effect and electrostatic interactions in hemoglobin.

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Abstract
Hb Cowtown [His HC3(146).beta. .fwdarw. Leu] exhibits high O2 affinity and a halved alkaline Bohr effect. X-ray analysis shows the COOH-terminal leucine to be in equilibrium between 2 positions: one with the salt bridge between the terminal carboxyl and Lys C5(40).alpha. intact and the leucyl side chain leaning against main chain atoms of helices F and FG and the other with the terminal salt bridge broken and the leucyl side chain touching Pro C2(37).alpha.. Structural changes are confined to the immediate neighborhood of the COOH terminus, showing the halving of the alkaline Bohr effect to be due directly to the loss of the histidine, without significant contributions from changes in pK values of other ionizable groups due to structural changes elsewhere.