Enzyme polyphenoloxidase , activity

DEVECE C, RODRIGUEZ LOPEZ J N, FENOLL L G, TUDELA J, CATALA J M, DE LOS REYES E and GARCIA CANOVAS F (1999) Enzyme inactivation analysis for industrial blanching applications comparison of microwave, conventional, and combination heat treatments on mushroom polyphenoloxidase activity , J g-nc Food Chem, 47 (11) 4506-11. 

Humic acids have been shown to slightly inhibit tyrosinase activity by complexing the enzyme (Ruggiero and Radogna, 1988). Allison (2006b) also demonstrated that the addition of humic acid to a soil significantly decreased the polyphenoloxidase activity of the soil. 

The addition of phenylthiourea to a preparation of the enzyme polyphenoloxidase completely inhibits the activity of the enzyme. 

In certain cases the production of extracellular enzymes can be used as an index of the amount of growth. For example, laccase (polyphenoloxidase) activities have been used to estimate growth of the myceUum of Agarkus biosporus in wheat straw [177]. 

Lee CY, Kagan V, Jaworski AW, Brown SK (1990) Enzymic browning in relation to phenolic compounds and polyphenoloxidase activity among various peach cultivars. J Agric Food Chem 38 99-101... 

Oliveira, J. C., Amorim, H. V., Silva, D. M., Teixeira, A. A., Polyphenoloxidase enzymic activity of four species of coffee beans during storage, Cientifica, 4, 114, 1976. (CA86 68577z)... 

Polyphenoloxidase (PPO, EC 1.14.18.1) is one of the most studied oxidative enzymes because it is involved in the biosynthesis of melanins in animals and in the browning of plants. The enzyme seems to be almost universally distributed in animals, plants, fungi, and bacteria (Sanchez-Ferrer and others 1995) and catalyzes two different reactions in which molecular oxygen is involved the o-hydroxylation of monophenols to o-diphenols (monophenolase activity) and the subsequent oxidation of 0-diphenols to o-quinones (diphenolase activity). Several studies have reported that this enzyme is involved in the degradation of natural phenols with complex structures, such as anthocyanins in strawberries and flavanols present in tea leaves. Several polyphenols... 

Laccase is one of the main oxidizing enzymes responsible for polyphenol degradation. It is a copper-containing polyphenoloxidase (p-diphenoloxidase, EC 1.10.3.2) that catalyzes the oxidation of several compounds such as polyphenols, methoxy-substituted phenols, diamines, and other compounds, but that does not oxidize tyrosine (Thurston, 1994). In a classical laccase reaction, a phenol undergoes a one-electron oxidation to form a free radical. In this typical reaction the active oxygen species can be transformed in a second oxidation step into a quinone that, as the free radical product, can undergo polymerization. 

When soybean leaves and pine needles were exposed to ozone, there was an initial decrease in the levels of soluble sugars followed by a subsequent increase. Ozone exposure also caused a decrease in the activity of the glycolytic pathway and the decrease in the activity was reflected in a lowered rate of nitrate reduction. Amino acids and protein also accumulated in soybean leaves following exposure. Ozone increased the activities of enzymes involved in phenol metabolism (phenylalanine ammonia lyase and polyphenoloxidase). There was also an increase in the levels of total phenols. Leachates from fescue leaves exposed to ozone inhibited nodulation. 

The metabolism of phenolics is regulated by the activity of various enzymes. As indicated above, the main and determining enzyme of phenolic synthesis is PAL, while in oxidation processes, the enzymes involved are peroxidase (POD) and primarily polyphenoloxidase (PPO). 

The results show that in all experimental conditions the enzyme activity loss was lower than 15%. When compared to the work presented by Habulin and Knez (8), this activity loss is considered low. Some works available in the literature point to the use of SCC02 as a satisfactory medium to inactivate some enzymes (8,9). It is important to mention that all these works used enzymes in native form, and the results presented herein are related to an immobilized enzyme (Novozym 435). On the other hand, our results are in perfect agreement with those obtained by Castellari et al. (9) for the system containing a polyphenoloxidase present in grape musts. 

Wild-Altamirano, C. (1 969) Enzymic activity during growth of vanilla fruit. 1. Proteinase, glucosidase, peroxidase and polyphenoloxidase. Journal of Food Science 34, 235-238. 

Figure 1-28 Enzymic Browning in the System Polyphenoloxidase-Cellulose-Catechol at 25 C and Different Water Activities. Lower aw values were changed to 0.70 after 9 days. Source From L. Acker, Water Activity and Enzyme Activity, Food Technol., Vol. 23, pp. 1257-1270,1969.

They can react with metal-containing enzymes (e.g., polyphenoloxidase and ascorbic acid oxidase) to form a copper-dithiocarbamate complex with high fungicidal activity (thiram and ziram probably owe their fungicidal activity to this type of reaction). 

Enzyme treatment of fruit pulp before pressing improves the yield and the colour. Pectin in soft fmits forms a gel-like mass which is very difficult to press. Treatment with pectinase leads to a thin, free rurming liquid and good pressable pulp. Since some of the pectinase are inhibited by polyphenols, activation of polyphenoloxidase which is present in fmits, is an important aspect of pulp treatment and can be achieved by aeration of the pulp. 

Certain enzymes present in grapes are responsible for wine problems such as clouding, darkening or an oxidized taste. To prevent this, wineries routinely treat must and wines with sulfur dioxide. In addition to its antimicrobial activity, SO2 has an antioxidative property which prevents browning and taste defects. Polyphenoloxidase has detrimental effects on wine quality. However enzymes are also responsable for the formation of certain desir able esters which are essential to the aroma or bouquet of the wine. 

Rastogi et al. (1999) studied the combined effect of high pressure (100-600MPa) with heat treatment (0°C-60°C) on inactivation of endogenous enzymes in order to develop shelf-stable red grape juice. The lowest peroxidase (55.75%) and polyphenoloxidase (41.86%) activities were found at 60°C, with pressures at 600 and 100MPa, respectively. 

In cereals, polyphenoloxidases preferably occur in the outer layers of the kernels. Wheat enzymes that exhibited cresol activity only (cf. 2.3.3.2) and were known as tyrosinases have been separated from polyphenoloxidases by chromatography and preparative gel electrophoresis. Polyphenoloxidases can cause browning in whole-meal flours. 

The polyphenoloxidase, tyrosinase, is a widely distributed enzyme found in plants and animals. It is the enzyme responsible for the formation of melanin pigments from phenylethylamine derivatives such as tyrosine and the catecholamines. According to Mason, it is a mixed function oxidase with two independent catalytic activities the hydroxylation of tyrosine to DOPA and the subsequent oxidation of DOPA, or another catechol derivative, to an open-chain quinone (cf. 12), which is then converted non-enzymati-cally to melanin [48-51]. 

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