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Oxidoreductase

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Oxidoreductase

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Oxidoreductase

  1. 1. Oxidoreductase Prof. Harshraj. S. Shinde K. K. Wagh College of Agril. Biotech, Nashik. India
  2. 2. Introduction • Oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule to another. • The reductant is called as electron donor. • The oxidant, also called the electron acceptor. • This group of enzymes usually utilizes NADP or NAD+ as cofactors.
  3. 3. Example • For example, an enzyme that catalyzed this reaction would be an oxidoreductase: • A– + B → A + B– • In this example, A is the reductant (electron donor) and B is the oxidant (electron acceptor) • Pi + glyceraldehyde-3-phosphate + NAD+ → NADH + H+ + 1,3-bisphosphoglycerate • In this reaction, NAD+ is the oxidant (electron acceptor), and glyceraldehyde-3-phosphate is the reductant (electron donor).
  4. 4. Glucose oxidase • The glucose oxidase enzyme (GOx) is an oxido-reductase that catalyses the oxidation of glucose to hydrogen peroxide and D- glucono lactone. • In cells, it aids in breaking the sugar down into its metabolites. • In order to work as a catalyst, GOx requires a cofactor, flavin adenine dinucleotide (FAD). FAD is a common component in biological oxidation-reduction (redox reactions).
  5. 5. Source of glucose oxidase • Most common source of glucose oxidase is Aspergillus niger
  6. 6. Applications of glucose oxidase • Glucose oxidase is widely used for the determination of free glucose in body fluids (diagnostics) • Glucose oxidase is found in honey and acts as a natural preservative. GOx at the surface of the honey reduces atmospheric O2 to hydrogen peroxide (H2O2) which acts as an antimicrobial barrier • GOx similarly acts as a bactericide in many cells (fungi, immune cells).
  7. 7. Cont….. • Glucose oxidase removes D-glucose from egg white to prevent browning. • GOx also used to monitor glucose levels in fermentation, bioreactors, and to control glucose in food products.
  8. 8. Glucose assay • In the glucose oxidase assay, the glucose is first oxidized by glucose oxidase to produce gluconate and hydrogen peroxide. • The hydrogen peroxide is then oxidatively coupled with a chromogen to produce a colored compound • which is then measured spectroscopically at 505nm.
  9. 9. Catalase • Catalase catalyzes the decomposition of hydrogen peroxide to water and oxygen. • It is a very important enzyme in protecting the cell from hydrogen peroxide • Catalase has one of the highest turnover numbers of all enzymes; one catalase molecule can convert approximately 5 million molecules of hydrogen peroxide to water and oxygen each second.
  10. 10. Cont… • Catalase is a tetramer of four polypeptide chains, each over 500 amino acids long • It contains four porphyrin heme (iron) groups that allow the enzyme to react with the hydrogen peroxide • he pH optimum for other catalases varies between 4 and 11 depending on the species. The optimum temperature also varies by species.
  11. 11. History of Catalase • Catalase was not noticed until 1818 when Louis Jacques Thénard, who discovered H2O2 (hydrogen peroxide), suggested its breakdown is caused by an unknown substance. • In 1900, Oscar Loew was the first to give it the name catalase • In 1937 catalase from beef liver was crystallised by James B. Sumner
  12. 12. Reaction of catalase • The reaction of catalase in the decomposition of hydrogen peroxide in living tissue: • 2 H2O2 → 2 H2O + O2. • The presence of catalase in a microbial or tissue sample can be tested by adding a volume of hydrogen peroxide and observing the reaction. • The formation of bubbles, oxygen, indicates a positive result.
  13. 13. Application • Catalase is used in the food industry for removing hydrogen peroxide from milk prior to cheese production. • Removing hydrogen peroxide from fabrics to make sure the material is peroxide-free to prevent browning
  14. 14. Polyphenol oxidase • Polyphenol oxidase (PPO) also known as monophenol monooxygenase tetramer that contains four atoms of copper per molecule • PPO causes the rapid polymerization of quinones to produce black, brown or red pigments (polyphenols) that cause fruit browning. • The amino acid tyrosine contains a single phenolic ring that may be oxidised by the action of PPOs to form o-quinone. Hence, PPOs may also be referred to as tyrosinase.
  15. 15. Source of Polyphenol oxidase • Enzyme mainly present in plastid (chlroplast) • Common plant food examples producing the enzyme are mushrooms, apples and lettuce
  16. 16. Application of Polyphenol oxidase • Used to remove toxic phenol (pollutant) • To remove toxic pesticides from food product
  17. 17. L-ascorbate oxidase • L-ascorbate oxidase is an enzyme that catalyzes the chemical reaction • 2 L-ascorbate + O2 2 dehydroascorbate + 2 H2O • Thus, the two substrates of this enzyme are L- ascorbate and O2, whereas its two products are dehydroascorbate and H2O. • This enzyme participates in ascorbate metabolism. It employs one cofactor, copper.
  18. 18. Applications of L-ascorbate oxidase • Ascorbate Oxidase is useful for enzymatic determination of ascorbic acid and for • Enzyme also used in elimination of ascorbic acid in clinical analysis.
  19. 19. MCQs
  20. 20. • ….. Is the most commonly used electron acceptor • NAD • FAD • NADH • FADH
  21. 21. • ….. Enzyme has the highest turnover number • Ascorbate oxidase • Catalase • Glucose oxidase • Amylase
  22. 22. • Most common source of glucose oxidase is … • E. Coli • Aspergillus niger • Glucose oxidizing bacteria • Fig
  23. 23. • ……removes D-glucose from egg white to prevent browning • GOx • Glucose oxidation • Peroxidase • PPO
  24. 24. • ….enzyme requires Cu as a cofactor • PPO • GOx • Catalase • Both a and b
  25. 25. • Term catalase was coined by • Louis Jacques Thénard • Oscar Loew • James B. Sumner • Jacobs Monod
  26. 26. • ….is the chloroplastic enzyme • PPO • GOx • Catalase • Peroxidase

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