J. Biol. Chem., Vol. 261, Issue 19, 8805-8810, Jul, 1986
Sulfhemoglobin. Properties of partially sulfurated tetramers
CM Park, RL Nagel, WE Blumberg, J Peisach and RS Magliozzo
The properties of sulfhemoglobin (sulfHb) were investigated using disc gel
isoelectric focusing and optical spectrophotometry. Laboratory- prepared
samples, which contained a high yield of sulfHb (70-85%), and a
patient-derived sample, which contained a low yield (12%), contain a
tetrameric population that reflects a random distribution of modified
(sulfurated) subunits. Hybrid tetramers, i.e. those containing sulfurated
and unmodified subunits, were resolved from fully sulfurated and unmodified
hemoglobin upon electrofocusing of ferric or ferrous sulHb samples. The
electrophoretic differences between ferric sulfHb and metHb arise from a
difference in the pK for the met to hydroxymet conversion of sulfurated
subunits (Carrico, R., Peisach, J., and Alben, J. O. (1978) J. Biol. Chem.
253, 2386-2391). Both partially and fully sulfurated tetramers, when in the
deoxy form and when in the fully ligated CO form, co-focus with their
unmodified deoxy-Hb and Hb CO counterparts. Thus, these sulfurated
tetramers exhibit normal ligand- dependent ionization of Bohr protons. In
air-equilibrated samples, hybrid tetramers are partially ligated as a
result of the reduced O2 affinity of the sulfurated subunits. These
partially ligated tetramers exhibit a pI intermediate between oxy-Hb and
deoxy-Hb due to the fractional ionization of Bohr protons. The partially
sulfurated, partially ligated tetramers as well as deoxy-sulfHb tetramers
were found to bind 2,3-diphosphoglycerate in disc gels. Despite the
preservation of these heterotropic effects, which are confirmed in CO
binding studies in solution, fully sulfurated tetramers recovered using
preparative isoelectric focusing exhibit little or no cooperativity.