Peroxidase activity of germinating Sorghum bicolor grains: effect of some cations

We investigated some properties of the major ionic peroxidase (POD) from germinating Sorghum bicolor var Fara Fara. Peroxidase activity increased eightfold during the first 36 h of germination and declined thereafter to four times the value in the dry grain after 144 h. Gel filtration followed by ion exchange chromatography resolved the major peroxidase into two forms. The predominant POD had an optimum temperature of 55 °C, two pH optima at 5.0 and 7.0, with a sharp decline in activity below pH 4.5, an apparent activation energy of 463 kJ mol−1, an apparent molecular weight of 63.1 kDa and was relatively heat-stable up to 70 °C. The enzyme was strongly inhibited by dithiothreitol and sodium metabisulphite. Calcium chloride and magnesium chloride below 2 mM enhanced POD activity without any adverse effect on germination, while ammonium chloride and ferric chloride inhibited the enzymatic activity of both forms. At 5 mM, magnesium chloride inhibited POD activity by 50% with only a 14% reduction in germination, while calcium chloride achieved the same effect at 10 mM. These results are pertinent to controlling the undesirable activity of peroxidase in a typical malting or brewing process.