Specific modification of the α chain C-terminal carboxyl group of hemoglobin by trypsin-catalyzed hydrazinolysis

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Abstract
In human deoxyhemoglobin a salt bridge links the .alpha. carboxyl of Arg-141 of each .alpha. chain to the .epsilon.-amino group of Lys-127 of the opposite .alpha. chain. These salt bridges are believed to contribute to the constraints in the quaternary deoxy (T) structure that lower its O2 affinity. This hypothesis was tested by incubating Hb with 2 M hydrazine and trypsin which catalyzes specifically the reversible hydrazinolysis of the .alpha. carboxyl of Arg-141.alpha.. X-ray analysis shows the major structural difference between native deoxyhemoglobin and hydrazide deoxyhemoglobin to be the loss of the Arg-141.alpha.1-Lys-127.alpha.2 salt bridge and its Arg-141.alpha.2-Lys-127.alpha.1 counterpart. Accurate O2 equilibrium curves of hydrazie Hb show that blocking of the salt bridge has raised the O2 affinity of the T structure while leaving that of the quaternary oxy (R) structure unchanged.

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