Alkaline low spin form of sulfite reductase hemeprotein subunit

The reversible reduction and reoxidation of Escherichia coli sulfite reductase hemeprotein subunit at pH 9.9 produces high and low spin ferric species, the latter with properties distinct from any alkaline low spin yet reported. With virtually no effect on the 298 degrees K optical spectrum, chloride drastically reduces the low spin EPR intensity and produces a high spin conformer pattern like that seen at pH 11. The distribution of g = 5 and g = 2.29 species in the doubly-reduced enzyme is also pH-sensitive.