Kinetic studies on veratryl alcohol transformation by horseradish peroxidase

A number of peroxidases, such as lignin peroxidase and manganese peroxidase have proved to be useful for industrial applications. Some studies on the effects of temperature and pH stability have been carried out. It is known that veratryl alcohol increases their stability in the range 28-50 degreesC and is oxidized, leading to veratryl aldehyde formation. Similar results w ith horseradish peroxidase (HRP) in the presence of cofactors were found, b ut the oxidation of veratryl alcohol in the absence of cofactors was extrem ely labile at acid pH and inactivated in a few minutes. Considering the gro wing industrial application of HRP, knowledge of its stability and denatura tion kinetics is required. In this study, horseradish peroxidase pool (HRP- VI) and its isoenzymes HRP-VIII (acid) and HRP-IX (basic) have been shown t o catalyze the oxidation of veratryl alcohol to veratryl aldehyde in the pr esence of hydrogen peroxide at pH 5.8 in the 35-45 degreesC range and in th e absence of any cofactors. Heat and pH denaturation experiments in the pre sence and absence of veratryl alcohol incubation were conducted with HRP-VI and HRP-IX isoenzymes. HRP-IX was the most active isoenzyme acting on vera tryl alcohol but HRP-VI was the most stable for the temperature range teste d. At 35 degreesC the HRP pool presented decay constant (K-d) values of 5.5 x 10(-2) h(-1) and 1.4 10(-2) h(-1) in the absence and presence of veratry l alcohol, respectively. with an effective ratio of 3.9. These results pres ent a new feature of peroxidases that opens one more interesting applicatio n of HRP to industrial processes. (C) 2001 Elsevier Science B.V. All rights reserved.