Peroxidase-Like Catalytic Activity of Aqueous- and Immobilized-Mn3+-octabromo-porphyrins on Ion-Exchange Resin Supplied as Mimetic of Horseradish Peroxidase

Abstract

In order to explore the capability of metal porphyrins as an alternative of horseradish peroxidase (HRP), HRP-like activity of three manganese-porphyrins (Mn-Ps) and three Mnoctabromo-porphyrins (Mn-OBPs) was examined in both aqueous and immobilized states. It was found that Mn 3؉-octabromotetrakis(1-methyl-pyridinium-4yl)porphine (Mn-OBTMPyP) has an activity of at least 90% of HRP in an aqueous solution. Mn-OBTMPyP exhibited a catalytic activity even in the presence of hydrogen peroxide without suicide reaction. In addition, Mn-OBTMPyP was revealed to function as an alternative to HRP in the quantitative determination of serum uric acid. These results are of great interest because they indicate that metal-octabromo-porphyrins possibly include promising candidates of artificial enzyme capable of substituting for HRP.Key words horseradish-peroxidase; mimetic; manganese-porphyrin; brominationThe metal-porphyrins (M-Ps) constitute the active center of enzymes such as catalase and horseradish peroxidase (HRP) used frequently in the clinical chemistry, and their HRP-like catalytic activities have long been investigated. 1)Generally, M-Ps have been regarded to be unavailable as a catalyst in an aqueous solution, because the HRP-like activity is accompanied by a suicide reaction which results in the decomposition of M-Ps.2,3) To avoid the suicide reaction, MPs of immobilized state have been developed and reported to be useful as an enzyme mimetics. [4][5][6][7] The authors also have reported that M-Ps immobilized ion-exchange-resins or -glass-beads have a practical use in the flow injection analyses as a solid mimetic of catalase or HRP. [8][9][10][11][12] However, those solid mimetics are not practically applicable to the batch method because of troublesome procedures required for the separation and the like.Recently, metal-octabromo-porphyrins (M-OBPs), which are resistant to oxidation, have been developed and elucidated their physical properties [13][14][15][16][17] as well as enzyme-like catalytic activities such as P450-, 18) superoxide dismutase- 19) and peroxidase-like catalytic activities on an organic-hydroperoxide. 20) In the present study, we examined the HRPlike activities of six different ionic manganese-porphyrins (Mn-Ps) and Mn-OBPs (see Fig. 1) in both the aqueous state and the solid-state wherein the substance was immobilized on ion-exchange-resin for the purpose of evaluating the capability as an artificial enzyme substituting for HRP. Based on the results, we then examined the applicability of a Mn-OBP, which showed a catalytic activity in a solution, to clinical chemistry. ExperimentalMn-tetrakis(4-sulfophenyl)porphine (Mn-TSPP) was prepared according to the method of Pasternack et al. 21) from commercially available H 2 -TSPP and MnCl 2 · 4H 2 O as an aqueous solution. Mn-TMPyP was prepared in the following manner. A mixture of commercially available H 2 -TMPyP and MnCl 2 · 4H 2 O in sodium acetate solution was refluxed for 3 h, followed by addition of sodium perchlorate solution to precipitate Mn-...