A multiphase 113Cd NMR investigation of metalloporphyrin reorientation in cadmium-substituted myoglobin.

113Cd NMR spectroscopy in both the solution and solid state has been used to investigate the role of the metal ion and the proximal histidine on metalloporphyrin reorientation in myoglobin. Heme disorder has been known to exist for many years but understanding its mechanism has proved difficult due to the short-lived nature of the minor porphyrin isomer in native myoglobin. Cadmium-substituted myoglobin can be generated in one form which contains different insertion isomers or in another form which contains predominantly only one of these species. This allows for direct investigation of heme disorder in metal-substituted myoglobin.