Comparative study of horseradish mutant forms by radioenzymology

Radioenzymology was used to study the recombinant and mutant forms of horseradish peroxidase, namely, F221W, Q176E, Q176A, S35K, E64P, E64S, S35A, and S35KQ176E. Both removal of the Trp residue and introduction of an additional one result in a simpler dose response; the insertion of polar residues stabilizes the enzyme molecule through realization of a more closed conformation. The greatest oscillation changes were found for the replacement by Ala. It was assumed that the binding site of guaiacol as a substrate is located near the residue 64, which is structurally related to the residue 176 and the heme. A scheme of formation of the intermediate through rotation of the Trp aromatic ring was proposed.