ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 85 Number 4
Differential response in kinetic properties of peroxidase in heat tolerant and susceptible cultivars of wheat grains
Peroxidase from actively metabolizing stage of developing wheat grains of two cultivars (cvs) namely C 306 and WH 542 was isolated and purified to 44.75 fold and 41.07 fold respectively, by employing ammonium sulphate precipitation, gel fdteration on Sephadex G-150 and ion exchange chromatography using DEAE-cellulose column chromatography. Optimum pH for enzyme activity was 4.0 for WH 542 and 6.0 for C 306. Peroxidase from C 306 exhibited greater heat stability (40°C) compared to WH 542 (30°C). By employing photo-oxidation and by studying the effect of pH on Km and Vmax, the involvement of histidyl and carboxyl groups in the active site of the enzyme was indicated. Enzyme inhibition by iodine and regeneration by mercaptoethanol indicated the presence of a thiol group. Modulation of enzyme activity in the presence of metal ions like Cd2+ , K+ , Ni2+ , Ca2+ , Zn2+and Na2+ indicated differential responses of peroxidase in these cultivars, which also showed varied effects with respect to thermodynamic properties like energy of activation (Ea), enthalpy change (?H) and entropy change (?S).
Keywords: Heat tolerance, kinestics, peroxidase, thermodynamic properties, wheat