Apple, ascorbate oxidase

Pizzocaro F Torreggiani D and Gilardi G. 1993. Inhibition of apple polyphenol oxidase (PPO) by ascorbic acid, citric acid and sodium chloride. J Food Proc Preserv 17 21—30. 

Ascorbate oxidase is mostly found in the peripheral part of the plant, as shown in Figure 1 for cauliflower and apple that had been cut through the middle and pressed on a piece of paper coated with a solution of L-ascorbate and the redox dye dichloroindophenol (14). The close association with the cell-wall material gives some support to the theory that the enzyme might be important for plant growth and ripening of... 

Figure 1. Peripheral location of ascorbate oxidase in cauliflower (left) and apple (right). The fruit was cut through the middle and pressed onto a piece of filter paper soaked with a mixture of i.-ascorbate and dichloroindophenol,...

Figure 33 Ribbon diagram of the monomer structure of ascorbate oxidase (PDB-code 1AOZ) prepared with MOLSCRiPT (P. J. Krauiis, J. Appl. Crystallogr. 1991,24, 946-950) and RASTER3D (E. A. Merritt M. E. P. Murphy, Acta Crystallogr., Sect D Biol. Crystallogr. 1994, 50, 869-873).

Electrochemical immobilization of ascorbate oxidase in poty(3,4-ethylenedio5q4 hiophene)/multiwalled carbon nanotubes composite films,/. Appl. Polym. Sci., 122, pp. 1142-1151. 

Marques, I. D. H. C., E. T. A. Marques, A. C. Silva, W. M. Ledingham, E. H. M. Melo, V. L. da Silva, and J. L. Lima Filho. 1994. Ascorbic acid determination in biological fluids using ascorbate oxidase immobilized on alkylamine glass beads in a flow injection potentiometric system. Appl. Biochem. Biotechnol. 44 81-89. 

The amino acid sequence predicted from pTOM13 shows a significant similarity to flavanone-3-hydroxylase, which requires Fe and 2-oxoglutarate [96]. Ververidis and John [98] applied the conditions to stabilise flavanone-3-hydroxylase to extract EFE from melon fruits and found that authentic EFE activity was recovered in a soluble fraction in the presence of Fe and ascorbate. This finding allowed other researchers to extract authentic EFE from apple [100,136,137] and avocado [99]. The molecular size of extracted ACC oxidase was about 35 kDa in both SDS-PAGE and gel filtration. This result indicates that ACC oxidase is a monomeric enzyme, and isolated cDNA clones represented by pTOM13 encode the entire ACC oxidase. 

Polyphenol oxidases and ascorbic acid oxidase, which occur in food, are known to have a Cu /Cu redox system as a prosthetic group. Polyphenol oxidases play an important role in the quality of food of plant origin because they cause the enzymatic browning for example in potatoes, apples and mushrooms. Tyrosinases, catecholases, phenolases or cresolases are enzymes that react with oxygen and a large range of mono and diphenols. 

Sondey S.M., Seib P.A., El-Atawy Y.S. Control of enzymatic browning in apple with ascorbic acid derivatives, polyphenol oxidase inhibitors, and complexing agents. Journal of Food Science, 53 997-1002 (1989). 

---