Characterization and kinetics studies of water buffalo (Bubalus bubalis) myoglobin

It is generally accepted that dry-aged buffalo (B. bubalis) meat becomes dark faster than bovine (B. taurus) meat, discouraging consumer purchase. We have investigated whether this faster darkening process might depend on structural and/or kinetic differences between buffalo and bovine myoglobins (Mbs). To this end, we have purified to homogeneity buffalo Mb from Longissimus dorsi muscle and obtained both its Mr (17,034.5) and the complete amino acid sequence, which, compared with the bovine one, showed three amino acid substitutions: Dbo141Ebu, Abo19Tbu and Abo117Dbu. As revealed by the 3D structure, they were located on the surface of the protein, far from the heme binding pocket, and did not cause appreciable structural changes. Autoxidation rates of purified buffalo and bovine myoglobins at 37 °C, pH 7.2, were almost identical (0.052±0.001 h-1 and 0.054±0.002 h-1, respectively), as were their oxygen-binding Kd values (3.7±0.1 μM and 3.5± 0.1 μM, respectively). These data indicate that the structure of the heme pockets in the two proteins is similar, with similar functional properties. Moreover, the percent of MetMb values in the purified buffalo and bovine samples, after the same time from slaughtering, were almost identical (57% and 47%, respectively). The results presented here suggest that the faster darkening of buffalo meat depends on factors other than the oxidation rate of its Mb, as, for example, the Mb content (0.393±0.005 g/100 g) and consequently its MetMb content, which is almost twice as high as bovine meat (0.209±0.003 g/100 g), and likely other factors.