Citation

Aitken MD, Heck PE. Biotechnol. Prog. 1998; 14(3): 487-492.

Copyright

(Copyright © 1998, John Wiley and Sons)

DOI

10.1021/bp980034z

PMID

unavailable

Abstract

Coprinus cinereus peroxidase (CIP) and other peroxidases are susceptible to mechanism-based inactivation during the oxidation of phenolic substrates. The turnover capacity (defined as the molar or mass concentration of substrate oxidized per unit concentration of enzyme inactivated) of CIP was quantified for phenol and 11 monosubstituted phenols under conditions in which enzyme inactivation by mechanisms involving hydrogen peroxide alone were minimized. Turnover capacities varied by nearly 2 orders of magnitude (absolute values on the order of 105-106 on a molar basis), depending on the substituent. On a mass basis, the enzyme consumption corresponding to the lowest turnover capacities is considerable and may influence the economic feasibility of proposed industrial applications of peroxidases. Within a range of substituent electronegativity values, molar turnover capacities correlated well (r2 = 0.89) with substituent effects quantified by radical σ values and semiquantitatively with homolyric O-H bond dissociation energies of the phenolic substrates, suggesting that phenoxyl radical intermediates are probably involved in the suicide inactivation of CIP. The correlation range in each case did not include phenols with highly electronwithdrawing (nitro and cyano) substituents because they are not oxidized by CIP, nor phenols with highly electron-donating (hydroxy and amino) substituents because they led to virtually complete inactivation of the enzyme with minimal substrate removal in the latter case we conclude that inactivation of CIP during the oxidation of hydroxy and amino-substituted phenols occurs by a different mechanism than that of the other phenolic substrates.; Coprinus cinereus peroxidase (CIP) and other peroxidases are susceptible to mechanism-based inactivation during the oxidation of phenolic substrates. The turnover capacity (defined as the molar or mass concentration of substrate oxidized per unit concentration of enzyme inactivated) of CIP was quantified for phenol and 11 monosubstituted phenols under conditions in which enzyme inactivation by mechanisms involving hydrogen peroxide alone were minimized. Turnover capacities varied by nearly 2 orders of magnitude (absolute values on the order of 105-106 on a molar basis), depending on the substituent. On a mass basis, the enzyme consumption corresponding to the lowest turnover capacities is considerable and may influence the economic feasibility of proposed industrial applications of peroxidases. Within a range of substituent electronegativity values, molar turnover capacities correlated well (r2 = 0.89) with substituent effects quantified by radical σ values and semiquantitatively with homolytic O-H bond dissociation energies of the phenolic substrates, suggesting that phenoxyl radical intermediates are probably involved in the suicide inactivation of CIP. The correlation range in each case did not include phenols with highly electron-withdrawing (nitro and cyano) substituents because they are not oxidized by CIP, nor phenols with highly electron-donating (hydroxy and amino) substituents because they led to virtually complete inactivation of the enzyme with minimal substrate removal. In the latter case we conclude that inactivation of CIP during the oxidation of hydroxy- and amino-substituted phenols occurs by a different mechanism than that of the other phenolic substrates.

Language: en

Keywords

Activation energy; Coprinus cinereus; Coprinus cinereus peroxidase; Dissociation; Enzyme consumption; Enzyme immobilization; enzyme inactivation; Enzymes; Hydrogen bonds; Hydrogen peroxide; Oxidation; peroxidase; phenol; phenol derivative; Phenols; turnover capacity; Turnover capacity