Peroxidase is an enzyme that is used as a catalyst for the oxidation of hydrogen peroxide by any of several substrates. An enzyme is a protein produced by a living organism that speeds up reactions within the organism's cells. The activity of the enzyme is affected by factors such as pH and temperature. This means that the speed of oxidation varies with the acidity or alkalinity of the solution. The enzyme is inactive at certain pH levels and functions optimally at others. Peroxidase can be derived from many different plant sources.
Peroxidase obtained from horseradish roots functions optimally at a pH of 7.0. It has a molecular weight of 40,000 and an isolectric point of 7.2. Horseradish peroxidase displays a high degree of specificity, being active on hydrogen peroxide and a few other chemicals. It is inhibited by cyanide and sulphide, but these inhibitions are usually reversible. It is a stable enzyme and can be stored for several years at cool temperatures.
Effects of pH on Activity
The activity of the peroxidase enzyme is dependent on pH. It exhibits maximum activity at a pH between 6.5 and 7.0, depending on the source from which the peroxidase is derived. The activity of the enzyme is reduced when pH levels are increased or reduced from this optimal pH range. Peroxidase activity ceases at a pH of 2.5 or 8.5 to 9.5. Lower pH levels result in a more effective inactivation of the enzyme than do higher pH levels, meaning that acidic environments are more effective inhibitors of peroxidase activity than basic environments. The level of acidity or alkalinity required to inactivate the enzyme varies by the type of peroxidase used.
Peroxidase activity is responsible for the browning or discoloration of some fruits during storage. The effect of pH on peroxidase activity is important for agricultural applications, as it can provide useful information on what types of environments are most conducive to keeping fruit looking aesthetically pleasing and extending the shelf life in commercial settings. Inactivating the enzymes using acids or bases is more practical than using heat or cold, although both are often used in conjunction to achieve the best results during storage and transportation of the fruits from farm to market.
Scientific studies on the effects of pH on peroxidase are conducted by biochemists in both industrial and educational settings. The findings of their research have important practical applications to the international agricultural industries. There is ongoing research on the effects of oxidation of melatonin in plants and the relationship with peroxidases and pH levels. The products are believed to have anti-inflammatory properties and may find future applications in the healthcare industries.
- Worthington Biochemical Corporation; Peroxidase; Krystal; 2010
- Scientia Agricola; Effect of pH and Temperature on Peroxidase and Polyphenoloxidase Activities of Litchi Pericarp; Mizobutsi et al; 2010
- RCN.com: Enzymes; 2010
- Ingentaconnect:The Effect of pH on Horseradish Peroxidase...”; Ximenes et al.; 2007