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JBC, Vol. 251, Issue 2, 465-470, Jan, 1976
R. E. Benesch, S. Ikeda and R. Benesch
Hemoglobin tetramers which cannot split into alphabeta dimers, because they
are covalently cross-linked between the beta chains across the
polyphosphate binding site, form complexes with haptoglobin. The reaction
is biphasic as measured by fluorescence quenching and peroxidase activity.
A complex in which one of the alpha beta dimers of the cross-linked
hemoglobin is bound to one of the sites in the divalent haptoglobin
molecule, is formed reversibly during the initial fast phase. In the
subsequent slower step, this product then either polymerizes, adds another
cross-linked hemoglobin molecule or, in the presence of excess haptoglobin,
combines with a second haptoglobin molecule. This latter complex, in which
two haptoglobin molecules are bridged by a cross-linked hemoglobin
tetramer, can still combine with normal alpha beta dimers at the vacant
haptoglobin combining sites. In spite of the very low oxygen affinity of
the cross-linked hemoglobin, combination with haptoglobin shifts if oxygen
affinity to the very high value of the normal hemoglobin-haptoglobin
complex.
Reaction of haptoglobin with hemoglobin covalently cross-linked between the alpha beta dimers
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