Heat stable peroxidases from Vigna species (V)
Shoots of three landraces of a Vigna species from two climatic areas of Cameroon were evaluated for their content of heat-resistant peroxidases. The peroxidase activity in the three landraces was detected with a greater catalytic efficiency for oxidation of O-dianisidine relative to ABTS (2, 2'-azino-bis-(3- ethylbenzothiazoline-6-sulfonic acid) at pH 5. For example, with respect to the landrace named Vs1 in this study, Vmax/Km for O-dianisidine was around 0.68 compared to ABTS (0.01). The results revealed a great thermal stability of peroxidases of a landrace cultivated in the hotter northern part of Cameroon (average temperature of 29°C). Residual activity in this landrace was 67, 34 and 3.4% after preincubation for 1 h at 70, 75 and 80°C respectively. For this same landrace, peroxidase activity did not significantly reduce after pre-incubation for 1 week at 55°C and was more than 60% after 3 weeks at 55°C. After storage for 365 days at room temperature (25°C), peroxidase activity remained above 30% for all three Vigna landraces, but higher at 47% for Vigna from the hotter area. Such thermal stability of peroxidases was not observed in maize, beans or peanuts in this study. The addition of calcium chloride in the crude extract of the more resistant Vigna landrace led to a total inhibition of thermal inactivation, after pre-incubation for 10 min at 80°C. These findings make this Vigna landrace a source of highly useful peroxidases in biotechnology, especially as part of bench top diagnostic kits in Africa that do not require cold chains.
Key words: Vigna, peroxidase, shoots, thermal stability.