Thermal activation of peroxidase from tobacco leaf mesophyll cell walls

Cell wall-bound peroxidase isolated from tobacco leaf mesophyll cell walls was found to consist of two isoenzymes (P1 and P2). Each exists in the form of a single subunit with the same molecular weight (35 000) as determined by sodium dodecyl sulphate (SDS) polyacrylamide gel electrophoresis. Both isoenzymes exhibited maximum activities at 70 degrees. P1 increased to 265% and P2 to 140% of the activities assayed at 27 degrees; below this temperature the two isoenzymes had the same specific activity. On hydrolysis, P1 showed a carbohydrate content of 26.22% when the monosaccharides were analyzed by gas liquid chromatography; P2 gave 21.45%.