Kinetics properties of guaiacol peroxidase activity in Crocus sativus L. corm during rooting.

BACKGROUND Guaiacol peroxidases (GP) are haem-containing enzymes participating in many physiological processes in plants. The expression pattern of these enzymes is organ-specific and developmentally regulated. METHODS The presence of GP activity in extract samples, prepared from Crocus sativus L. corms that were either dormant or rooting for 3, 6 and 10 days, was investigated. RESULTS Kinetic studies revealed a significant similarity among GP activities detectable in the corm at different stages of development: in all extract samples, the activity was maximal at pH 7.5 and after preincubation at 30-40 degrees C. When guaiacol was used as the varying substrate, Michaelis-Menten kinetics behavior was observed in all extract samples and resulted in similar KM values; catalytic efficiencies were also very similar. The corm GP activity was inhibited by cyanide, azide and ascorbate. The GP activities from different extract samples had the same sensitivities to azide, cyanide and ascorbate and the type of inhibition by azide and cyanide was competitive and uncompetitive, respectively, while ascorbate inhibited the GP activity non-competitively. Corm extract samples from different stages of rooting similarly responded to temperature treatment and a biphasic Arrhenius plot resulted for each extract sample studied. When dormant, 3-, 6- and 10-days-rooting corm extracts were submitted to non-denaturing polyacrylamide gel electrophoresis, the GP-specific activity staining revealed one band on the gel, with the same migrating distances. CONCLUSION This finding in combination with kinetic studies demonstrated that at least one form of GP, with an apparent molecular weight of 68 kDa, was expressed during development of Crocus sativus L. corm.