Optimisation of soybean peroxidase treatment of 2, 4-dichlorophenol

Abstract

In the presence of hydrogen peroxide (H 2 O 2 ), peroxidase enzymes (PE) catalyse the oxidation of various chlorinated phenols to free radicals, which then combine to form insoluble polymers that precipitate out of solution. This study systematically characterises the treatment of 2,4-dichlorophenol (2,4-DCP) using soybean peroxidase (SBP) as an oxidising catalyst. The effects of pH, SBP concentration, polyethylene glycol (PEG) additive and initial chlorophenol concentration on 2,4-DCP treatments are reported. Optimum pH for removal of 2,4-DCP without PEG was pH 8.2. The pH operating range of SBP was from 2.5 to 9.4 which is wider than reported for horseradish peroxidase (HRP). A general equation is presented that describes the units of SBP required (without PEG) to treat a given amount of 2,4-DCP at the optimum pH of 8.2. Addition of PEG increased the effectiveness of SBP by factors of 10 and 50 for PEG-3350 and PEG-8000 respectively. A new pH optimum of 6.2 was also found when SBP was used with PEG. Batch and semi -batch enzyme delivery has also been identified as a crucial parameter for the SBP treatment process. The most effective addition scheme was based on five equal concentrations of SBP and H 2 O 2 over 15 min and 30 min intervals respectively compared to a single batch addition. This protocol was the most effective as it took advantage of limiting the amount of SBP and H 2 O 2 available at each step. This reduces the possible chance of SBP inactivation by excessive H 2 O 2 when using a single batch concentration. Average 2,4-DCP removals achieved were 83.5%, 75.5% and 71.5% for 100, 200 and 300 mg/l 2,4-DCP concentrations respectively compared to 62%, 52% and 58% for the single batch addition control.

Stabilizing and suicide-peroxide protecting effect of Ni2+ on horseradish peroxidase

“…For this reason, the enzyme used for phenol removal was incubated with an activatory concentration of Ni 2+ (2 mM). Similar results were reported for the effect of PEG on HRP stability [8][9][10][11][12]. In such a process, peroxidase can be inactivated by several mechanisms: I) Adsorption of polymerized phenol on peroxidase resulting in reduced access of a substrate to the enzyme's active site [30][31][32].…”

“…E-mail: nazarikh@ripi.ir be considered, and various techniques for reducing the role of suicide inactivation must be applied. Among such methods, the use of polyethylene glycol (PEG, with various molecular weights) has been reported to increase the stability and lifetime of the enzyme [8][9][10][11].…”

Biocatalytic properties of a peroxidase-active cell-free extract from onion solid wastes: caffeic acid oxidation

“…The temperature at which optimum activity was attained (30°C) is close to that found for BGP and HRP (Akhtar et al 2005;Bódalo et al 2006;Yamada et al 2007), which lied between 30°C and 40°C, and somewhat lower than TMP that showed an optimum between 40°C and 50°C (González et al 2006). By contrast, SBP has been reported to be much more active at 22 than at 4°C (Kennedy et al 2002), while other studies demonstrated that SBP is even more active at 80°C than at 20°C (Geng et al 2001).…”

“…Horseradish peroxidase is the most studied enzyme in this regard, and has been used mainly for the treatment of aqueous phenols and chlorophenols (Tatsumi et al 1996;Wu et al 1997;Tong et al 1998;Wagner and Nicell 2002;Cheng et al 2006;Dalal and Gupta 2007), but also other pollutants such as polychlorinated biphenyls (Singh et al 2000) and bisphenol A (Huang and Weber 2005). Crude and partly purified soybean peroxidase has also been used in the treatment of phenols and chlorophenols (Caza et al 1999;Flock et al 1999;Wilberg et al 2002;Kennedy et al 2002), and bitter gourd (Momordica charantia) peroxidase for the treatment of textile dyes (Akhtar et al 2005).…”

Potential applications of peroxidases

“…Recently, however, peroxidase from other sources such as soybean (Caza, Bewtra, Biswas, & Taylor, 1999;Kinsley & Nicell, 2000;Kennedy, Alemany, & Warith, 2002) and turnip (Duarte-Vazquez, Ortega-Tovar, Garcia-Almendarez, & Regalado, 2003), have been suggested as alternatives to horseradish. The peroxidase treatment process is still in the experimental stage.…”