Inhibition of horseradish peroxidase activity by thiol type inhibitors

The inhibition by cysteine and glutathione of 4-amino antipyrine oxidation by horseradish peroxidase was compared. The kinetics of the peroxidase inhibition by glutathione was investigated and compared to L-cysteine inhibition. IC50 for L-cysteine and glutathione was determined and used for the subsequent kinetics studies. The biological activity of the enzyme was measured in the presence of each inhibitor using 4-amino antipyrine as substrate. It was found that reduced glutathione was a more potent inhibitor on peroxidase activity than L-cysteine. Kinetic studies showed that inhibition was non-competitive and mixed type in both cases. The values of K-m and V-max in the presence of each inhibitor were also calculated. (c) 2005 Elsevier B.V. All rights reserved.