Trans effects in nitric oxide binding to myoglobin cavity mutant H93G

A synthetic myoglobin was created to study the formation of six-coordinate complexes in the presence of nitric oxide. When nitric oxide binds with the heme protein, it typically weakens the nearest bond between heme and iron. In contrast, the synthetic myoglobin contains imidazole that functions as a ligand for iron. The presence of nitric oxide breaks this bond to form a five-coordinate complex. The six-coordinate complex can only be formed in the presence of excess imidazole, which shows that it has a lower binding constant than nitric oxide for the heme.