Intracellular substrates of a heme-containing ascorbate oxidase in Pleurotus ostreatus

Abstract

A novel heme-containing ascorbate oxidase isolated from oyster mushroom, Pleurotus ostreatus, catalyzes oxidation of ascorbic acid (Kim et al., 1996). In this report, we describe the identification of intracellular substrates of the enzyme in the mushroom. Six compounds, which can serve as substrate of the heme-containing ascorbate oxidase, were identified as L-ascorbic acid, D-erythroascorbic acid, 5-O-(alpha-D-glucopyranosyl)-D-erythroascorbic acid, 5-O-(alpha-D-xylopyranosyl)-D-erythroascorbic acid, 5-methyl-5-O-(alpha-D-gluco-pyranosyl)-D-erythroascorbic acid, and 5-methyl-5-O-(alpha-D-xylopyranosyl)-D-erythroascorbic acid. All of the compounds were oxidized at a significant rate by the heme-containing ascorbate oxidase. Oxidation of the compounds produced equimolar amounts of hydrogen peroxide per mole of substrate.

Effect of light and reductones on differentiation of Pleurotus ostreatus

“…The concentration of hydrogen peroxide produced was quite similar to that of the reductones oxidized (Lee et al, 2009). It has been reported that ascorbate oxidase was detected only in the mycelial stage of development in P. ostreatus (Kim et al, 1996).…”

“…Ascorbic acid, erythroascorbic acid and an additional four reductones such as 5-O-(Į-glucopyranosyl)--erythroascorbic acid, 5-O-(Į--xylopyranosyl)--erythroascorbic acid, 5-methyl-5-O-(Į--glucopyranosyl)--erythroascorbic acid and 5-methyl-5-O-(Į--xylopyranosyl)--erythroascorbic acid have been identified in the fruit body of the oyster mushroom P. ostreatus and other basidiomycetes (Okamura, 1994;Lee et al, 2009). The enzymes involved in the ascorbate system were isolated from the vegetative mycelia of P. ostreatus and characterized.…”

“…Ascorbate oxidase containing heme as a prosthetic group, catalyzed the oxidation of ascorbic acid to dehydroascorbate and hydrogen peroxide was produced during the oxidation (Kim et al, 1996;Lee et al, 2009). Ascorbyl radical reductase was responsible for recovery of ascorbic acid from the ascorbyl free radical (Yu, 1999).…”

“…Synthetic sucrose-asparagine (SA) medium and complex yeast malt extract (YM) medium were used to determine a suitable nutrient condition for fruit body formation as described previously (Lee et al, 2009). The YM medium was composed of 3 g of malt extract, 3 g of yeast extract, 5 g of bacto-peptone, and 10 g of glucose per liter of distilled water.…”

“…Samples were frozen, thawed, and centrifuged. The supernatant was used for the determination of reductones as described previously (Lee et al, 2009). The supernatant was loaded onto two tandem-linked ODS hypersil columns (Hewlett Packard, 100 mm×4.6 mm), and chromatographed on a Waters 510 HPLC equipped with a 460 electrochemical detector.…”