Oxygen binding and nitric oxide dioxygenase activity of cytoglobin are altered to different extents by cysteine modification.

Cytoglobin (Cygb), like other members of the globin family, is a nitric oxide (NO) dioxygenase, metabolizing NO in an oxygen (O-2)-dependent manner. We examined the effect of modification of cysteine sulfhydryl groups of Cygb on its O-2 binding and NO dioxygenase activity. The two cysteine sulfhydryls of Cygb were modified to form either an intramolecular disulfide bond (Cygb_SS), thioether bonds to N-ethylmaleimide (NEM; Cygb_SC), or were maintained as free SH groups (Cygb_SH). It was observed that the NO dioxygenase activity of Cygb only slightly changed (similar to 25%) while the P-50 of O-2 binding to Cygb changed over four-fold with these modifications. Our results suggest that it is possible to separately regulate one Cygb function (such as O-2 binding) without largely affecting the other Cygb functions (such as its NO dioxygenase activity).