Isolation and properties of myoglobins from rat (Rattus norvegicus) skeletal muscles

One major (Mb I) and two minor (Mbs II and III) myoglobins, were isolated by a heat-denaturation-gel-filtration-chromato-focusing procedure from aqueous extract of rat skeletal muscles. The primary structure of the major component, as determined by an automatic Edman degradation method, revealed amino acid replacements at nine positions compared with murine myoglobin. As in murine myoglobin, a cysteine residue, highly reactive to p-chloromercuribenzoate (PMB), was present at position 66. The two minor components, with higher anodic mobilities and with SH group unreactive to PMB, were found to be derived from Mb I through mixed disulfide formation with cysteine (Mb II) or glutathione (Mb III) at the Cys66 residue. In view of the hydropathy profile, secondary structures of rat and mouse myoglobins showed few differences from each other. The three rat myoglobins displayed essentially identical oxygen equilibrium properties with neither homotropic nor heterotropic allosteric interactions, which agreed very well with those computed from the kinetic measurements.