JBC, Vol. 254, Issue 8, 2595-2599, Apr, 1979
Use of heme spin-labeling to probe heme environments of alpha and beta chains of hemoglobin
P. W. Lau and T. Asakura
A spin label attached to a propionic acid group of the heme has been used
to probe the heme environment of the alpha and beta chains of hemoglobin in
both the subunit and tetrameric forms. The electron paramagnetic resonance
(EPR) studies of hemoglobin hybrids in which the spin label is attached to
either the alpha- or beta-heme (alpha2SLbeta 2 or alpha2beta2SL) and
spin-labeled isolated chains (alphaSL and betaSL) show that: 1) alpha- and
beta-hemes have different environments in the tetrameric forms of oxy-,
deoxy-, and methemoglobins as well as in isolated single chains; 2) when
isolated subunits associate to form hemoglobin tetramers, the environment
of the alpha-heme changes more drastically than that of the beta-heme; 3)
upon deoxygenation of hemoglobin, the structure in the vicinity of the
alpha-heme changes more drastically than that of the beta-heme; and 4) upon
the addition of organic phosphates to methemoglobin, the change in the spin
state of the heme irons mainly arises from beta-heme. The results
demonstrate conclusively that the alpha and the beta subunits of hemoglobin
are structurally nonequivalent as are their structural changes as the
result of ligation. The relationship of EPR spectrum and structure of
hemoglobin is discussed.
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