The myoglobin of rodents Proechimys guairae (casiragua) and Mus musculus (house mouse)

Recombinant expression of Mus musculus myoglobin

The cDNA encoding for Mus musculus myoglobin (Mb) was amplified using standard RT-PCR techniques and cloned in an appropriate bacterial expression vector. For the first time, mouse Mb was recombinantly expressed in Escherichia coli cells, BL21(DE3), and purified in sufficient amounts to carry out a preliminary characterization. As shown by mass spectrometry, the protein is found in complex with glutathione, which binds the Cys residue in the topological position E9, in the proximity of the heme group. In recombinant murine Mb, azide affinities are only slightly dependent on the Cys(E9) oxidation state. This suggests that Cys(E9) does not provide a relevant contribution for the stabilization of ligands bound to the heme iron atom. Recombinant expression of M. musculus Mb might have an important role in order to investigate the eventual involvement of Cys(E9) in the new physiological roles proposed for Mb.

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.

Mixed disulphide formation in myoglobin of mouse (Mus musculus)

The myoglobin, isolated from murine skeletal muscles by chromatofocusing, showed the three components, one major and two minor, with different electrophoretic mobilities. The major component with the isoelectric point (pI) of 7.55 had one reactive SH/mole, while the others with pI of 7.32 and 7.16 showed none, which could be rendered fully reactive by treating the proteins with beta-mercaptoethanol. The three components were the same in their molecular weight (18 kDa), amino-acid composition with one Cys residue and oxygenation properties. By a sensitive high-performance liquid chromatography method, the occurrence of cysteine or glutathione mixed disulphide was verified in the two minor components. We conclude from these results and incubation experiments with low-molecular-weight thiols that the two minors were derived from the major by a mixed disulphide formation with either cysteine or glutathione of the cysteinyl SH at the 66th sequence.

Conformational free energy of armadillo metmyoglobin

The conformational free energy of armadillo metmyoglobin was examined over a pH range of 4.4-8.0 and a guanidinium chloride concentration of 0-2.3 M. For isothermal unfolding at 25 degrees essentially the same value was obtained for the conformational free energy from all the data: 27 +/- 2 kJ/mol. These data suggest that the armadillo has the least stable metmyoglobin of any mammal thus far examined. The cooperativity of the unfolding with respect to denaturant is considerably less than for other mammalian myoglobins. On unfolding only three to four side chains with a pKA of 6 in the unfolded protein are protonated instead of the six found for horse and sperm whale myoglobins.