Apples ascorbic acid 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. 

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. 

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). 

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. 

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