Abstract:

The optimum conditions affecting the hydrolysis activity of metmyoglobin reductase (MetMbase) from porcine cardiac muscle towards porcine metmyoglobin (MetMb) were determined with the equine MetMb purchased from Sigma Company as a standard marker using orthogonal array design, and the Michaelis equation and the enzyme kinetics were investigated as well. The results showed that pH, temperature and reaction time were three main important factors affecting the expression of MetMbase activity. At a given enzyme/substrate ratio in the reaction system, the optimum reaction conditions for the maximum expression of enzyme activity were as follows: pH 6.4, 35 ℃ and 30 min. When porcine MetMb was used as a substrate, the Michaelis equation was Y = 0.0004X + 0.0083 (R2 = 0.9948), the Michaelis constant (Km) 4.82 × 10-5 mol/L, and Vmax 120.48 nmol/min·g. In addition, this study also showed that the activity of the enzyme decreased in vitro when pH was below 6.0 or above 7.0 and a significant inhibition of activity was observed at low temperature. However, higher activity was seen when temperature was increased to 20 ℃ and no activity at higher temperature over 50 ℃. Our results prove that cold storage of fresh meat (4 － 10 ℃) is favorable to the stability of MetMbase activity and the color as well as its quality.

Key words: MetMbase, Michaelis equation, kinetics, porcine cardiac muscle