Tomato Peroxidase

Abstract

A major peroxidase has been found in the tomato pericarp (Lycopersicon esculentum var. Tropic) of the ripe and green fruit. A purification scheme yielding this enzyme approximately 85% pure has been developed. The tomato enzyme resembles horseradish peroxidase (HRP) in a standard peroxidase assay and in its ability to be reduced to ferroperoxidase, to be converted to oxyferroperoxidase (compound III), and to form peroxidase complexes with hydrogen peroxide (compounds I and II). In contrast to the HRP, the tomato peroxidase fails to catalyze the aerobic oxidation of indole-3-acetic acid in the presence of 2,4-dichlorophenol and manganese. The tomato peroxidase can be resolved into two nonidentical subunits in the presence of dithiothreitol while HRP remains as a single polypeptide chain after such treatment. Dithiothreitol is oxidized in the presence of tomato or horseradish peroxidase with the enzymes accumulating in their oxyferroperoxidase forms during the oxidation reaction. Whereas HRP returns to its free ferric form at the end of the reaction, the tomato enzyme is converted into a form that absorbs at 442 nanometers.A single peroxidase which has been shown to exist in tomato fruit extracts and to exhibit some IAA oxidase activity (5, 8) has been implicated both in the production of ethylene (12,17,18) and in the destruction of the plant growth hormone IAA (8). Although it is not unusual to relate the action of the enzyme peroxidase with the control of the above hormones, in the case of tomato fruit it is premature to assume such a relationship because of insufficient information about the physical and catalytic properties of this peroxidase and the lack of a purification method which would allow a quantitative estimation and a complete isozyme composition of the noncovalently bound peroxidases of the fruit (22, 23).Spectral properties and pH optima of the tomato fruit peroxidase in catalyzing the oxidation of redogenic substrates in the presence of H202 have been previously reported by Evans (6). The present report deals with additional properties of the purified enzyme including its capability to be converted to complexes of higher oxidation states (compounds I, II, III) which are thought to be important for the IAA oxidase activity of peroxidases (13,26). The enzyme HRP,3 a well studied peroxidase, was employed in order to compare some of its properties with similar properties of the tomato enzyme. ' cheesecloth, and the residue was washed twice with 100 ml of 0.1 M phosphate buffer (pH 6.5). The filtrates were combined and centrifuged at 2,000 g for 10 min. The supernatant, to be referred to as crude soluble peroxidase fraction, was stored at 0 C for further use. The pellet and the solid material on the cheesecloth were suspended in 200 ml of 0.2 M sodium maleate-0.2 M calcium chloride adjusted to pH 6.5. The suspension was then sonicated for 5 min and centrifuged at 2,000g for 10 min. Under this treatment peroxidases that were ionically bound to the tomato pulp were solubilized (17). These per...

Hydrogen Peroxide-mediated Oxidation of Indole-3-acetic Acid by Tomato Peroxidase and Molecular Oxygen

“…Tomato anionic peroxidase was extracted from tomato (Lycopersicon esculentum var. tropic) pericarp tissue and purified to about 85% homogeneity as previously described (11). Enzyme concentrations were estimated from the 403 nm A of solutions, using a millimolar extinction coefficient of 107 for the enzyme (11).…”

“…We have previously reported that tomato anionic peroxidase lacked the capacity to oxidize IAA in the presence of DCP4 and manganous ion as activators, while commercially purified HRP oxidized IAA effectively under the same conditions without a significant lag period (11). The inability of the tomato peroxidase to carry out the oxidation of IAA was then attributed to the low reactivity of the compound II form of the enzyme as compared to HRP compound II.…”

Morphological and biochemical responses of Oryza sativa L. (cultivar MR219) to ion beam irradiation

“…The specific activities of peroxidases of irradiated and non-irradiated plant samples were determined by the method of Kokkinakis and Brooks (1979). The oxidation of guaiacol by peroxidases in the presence of hydrogen peroxide (H 2 O 2 ) was used as the basis for the colorimetric assay based on the development of a reddish color (Doerge et al, 1997).…”

Anions Activate the Oxidation of Indoleacetic Acid by Peroxidases from Tomato and Other Sources

“…The fractions containing the major peak of peroxidase were combined, concentrated to 2 mL, and dialyzed against 0.02 M NaCl. This enzyme represents the main anionic peroxidase in tomato fruit (14,29 …”

“…The information on tomato peroxidase as an IAA oxidase has been particularly conflicting. Kokkinakis and Brooks (14) measured the oxidation of IAA in citrate buffer and found that the tomato enzyme was much less effective than horseradish peroxidase. They subsequently reported that the oxidation by tomato peroxidase was enhanced by the inclusion of peroxide in the reaction mixture (15).…”