PMID: 11330823May 2, 2001Paper

An essential role of active site arginine residue in iodide binding and histidine residue in electron transfer for iodide oxidation by horseradish peroxidase

Molecular and Cellular Biochemistry
S AdakR K Banerjee

Abstract

The objective of the present study is to delineate the role of active site arginine and histidine residues of horseradish peroxidase (HRP) in controlling iodide oxidation using chemical modification technique. The arginine specific reagent, phenylglyoxal (PGO) irreversibly blocks iodide oxidation following pseudofirst order kinetics with second order rate constant of 25.12 min(-1) M(-1). Radiolabelled PGO incorporation studies indicate an essential role of a single arginine residue in enzyme inactivation. The enzyme can be protected both by iodide and an aromatic donor such as guaiacol. Moreover, guaiacol-protected enzyme can oxidise iodide and iodide-protected enzyme can oxidise guaiacol suggesting the regulatory role of the same active site arginine residue in both iodide and guaiacol binding. The protection constant (Kp) for iodide and guaiacol are 500 and 10 microM respectively indicating higher affinity of guaiacol than iodide at this site. Donor binding studies indicate that guaiacol competitively inhibits iodide binding suggesting their interaction at the same binding site. Arginine-modified enzyme shows significant loss of iodide binding as shown by increased Kd value to 571 mM from the native enzyme (Kd = 150 mM). Alth...Continue Reading

Citations

Apr 22, 2006·Applied Microbiology and Biotechnology·Martin Hofrichter, René Ullrich
Mar 12, 2008·Acta Biochimica Et Biophysica Sinica·Xianping Chen, Karl-Heinz van Pée

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