Oxidoreductase

Oxidoreductase

1. Oxidoreductase Prof. Harshraj. S. Shinde K. K. Wagh College of Agril. Biotech, Nashik. India

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. 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 ) P i  + 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. 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. Source of glucose oxidase Most common source of glucose oxidase is Aspergillus niger

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 O 2  to hydrogen peroxide  (H 2 O 2 ) which acts as an antimicrobial  barrier GOx similarly acts as a bactericide in many cells (fungi, immune cells ).

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. 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. 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. 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. History of Catalase Catalase was not noticed until 1818 when  Louis Jacques Thénard , who discovered H 2 O 2  (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. Reaction of catalase The reaction of catalase in the decomposition of hydrogen peroxide in living tissue : 2 H 2 O 2  → 2 H 2 O + O 2. 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. 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. 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. Source of Polyphenol oxidase Enzyme mainly present in plastid ( chlroplast ) Common plant food examples producing the enzyme are mushrooms, apples and lettuce

16. Application of Polyphenol oxidase Used to remove toxic phenol (pollutant) To remove toxic pesticides from food product

17. L- ascorbate oxidase   L- ascorbate oxidase   is an  enzyme that catalyzes the chemical reaction 2 L- ascorbate + O 2    2 dehydroascorbate + 2 H 2 O Thus , the two substrates of this enzyme are L- ascorbate  and O 2 , whereas its two products are dehydroascorbate and H 2 O . This enzyme participates in  ascorbate  metabolism. It employs one cofactor, copper.

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. MCQs

20. ….. Is the most commonly used electron acceptor NAD FAD NADH FADH

21. ….. Enzyme has the highest turnover number Ascorbate oxidase Catalase Glucose oxidase Amylase

22. Most common source of glucose oxidase is … E. Coli Aspergillus niger Glucose oxidizing bacteria Fig

23. ……removes D-glucose from egg white to prevent browning GOx Glucose oxidation Peroxidase PPO

24. ….enzyme requires Cu as a cofactor PPO GOx Catalase Both a and b

25. Term catalase was coined by Louis Jacques Thénard Oscar Loew  James B. Sumner Jacobs Monod

26. ….is the chloroplastic enzyme PPO GOx Catalase Peroxidase