Red Cabbage (Brassica oleracea) as a New Source of High-Thermostable Peroxidase

Soluble and membrane-bound peroxidases (PODs) were extracted from red cabbage using Triton X-114. Optimum activity was obtained at pH 4.0 for both enzymes, and both were inactivated by sodium dodecyl sulfate (SDS). The K-M and V-m values for H2O2 were found to be 0.98 mM and 8.1 mu M/min, respectively, for soluble POD and 0.82 mM and 6.1 mu M/min, respectively, for membrane-bound POD. When the 2,2'-azinobis(3-ethylbenzothiazolinesulfonic acid (ABTS) concentration was increased, maintaining a steady concentration of H2O2, the activity was inhibited at the highest ABTS concentrations in soluble POD. Ascorbic acid was found to be the most active modulator of POD activity. The effect of cyclodextrins was also studied, and the complexation constant between ABTS and hydroxypropyl-beta-cyclodextrins (HP-beta-CDs) was calculated (K-c = 312 M-1). Membrane-bound POD is more thermostable than soluble POD, losing >90% of relative activity after 5 min of incubation at 76.6 and 30.2 degrees C, respectively.