JBC, Vol. 254, Issue 2, 371-376, Jan, 1979
Interaction of human apohemoglobin with inositol hexaphosphate
A. H. Chu and E. Bucci
Experiments of sedimentation velocity and equilibrium indicate that in the
presence of inositol hexaphosphate the degree of polymerization of
apohemoglobin is shifted in favor of the formation of tetramers, with a
maximum effect when the concentration of the polyphosphate is 1 mM. Above
this concentration, a redissociation of the system into dimers is promoted.
This phenomenon is probably due to the binding of inositol hexaphosphate to
apohemoglobin with a stoichiometry higher than 1 mol of polyphosphate/4
subunits. The optical rotatory dispersion spectrum of apohemoglobin is also
modified by its interaction with inositol hexaphosphate suggesting a small
increase in the helical content of the protein. Measurements of circular
dichroism in the near-UV region of the spectrum indicate that the
environment of the aromatic chromophores of the protein such as tyrosine,
phenyalanine, and tryptophan is not affected by the interaction. The
presence of inositol hexaphosphate decreases the rate of reaction of the
beta-93 cysteinyl residues of apohemoglobin with both p-mercuribenzoate and
N-ethylmaleimide, suggesting a conformational change of the protein also at
the level of its tertiary structure.
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