Covalent attachment of the heme to Synechococcus hemoglobin alters its reactivity toward nitric oxide

The reactivity of hemoglobin toward NO depends on the histidine-heme covalent linkage. In the crosslinked state, the ferrous globin binds NO to form a stable six-coordinate complex; in contrast, NO binding to the unmodified form inhibits crosslinking, causes heme dissociation, and, remarkably, undergoes reduction to produce HNO.85