Enzymes properties, nomenclature and classification

Enzymes - Definition, Introduction about biocatalysts, Properties of enzymes, Specificity, capacity for regulation, Example for enzyme at specific pH, Nomenclature of enzymes, Systematic name, common name, enzyme commission number, Classification of enzymes: Oxidoreductase, Transferase, lyases, ligases, isomerases, hydrolases.

1. Enzymes: Properties, Classification and Nomenclature Presented by: Jasmine Juliet Biochemistry, Agricultural College & Research Institute, Madurai.

2. Enzymes - Introduction Enzymes are biocatalysts present in cells that speed up biochemical reactions without getting itself destroyed in the reaction. All types of biochemical reactions in the cell require enzymes . Enzymes are typically proteins . C ertain types of RNA can also serve as catalysts. These RNA molecules are called ribozymes .

3. Characteristics of enzymes Enzymes being proteins exhibit all properties of proteins . They have their specific isoelectric points at which they are least soluble. They can be denatured by changes in pH and temperature. Higher reaction rate : The reaction rates of enzyme catalyzed reaction are very high and are 10 6 to 10 12 times higher than uncatalyzed reactions.

4. Characteristics of enzymes Milder reaction conditions : Enzymatic reactions occur at relatively low temperatures, below 100 o C, atmospheric pressure and nearly neutral pH.

5. Characteristics of enzymes Capacity for regulation: The catalytic activity and the amount of enzymes synthesized are highly regulated. The mechanisms of these regulatory processes include allosteric control, covalent modification of enzymes and feed-back inhibition.

6. Characteristics of enzymes Greater reaction specificity : Reactions catalyzed by enzymes are highly specific and three types of specificities are observed.

7. Characteristics of enzymes Absolute specificity: When enzymes catalyse only one particular reaction they are said to exhibit absolute specificity. Eg . Urease acts only on urea.

8. Characteristics of enzymes Group specificity : Enzymes acting on a group of substances that possess a particular type of linkage common to that group of substances is called group specificity . Eg . Enzyme acting upon starch, dextrin and glycogen which have the same type of glycosidic linkage.

9. Characteristics of enzymes Optical and stereo specificity : Almost all enzymes show a high degree of optical or stereo specificity. Optical specificity refers to enzymes acting on substances possessing same optical activity. Eg : α-Amylase acts on only α - glycosidic linkages.

10. Nomenclature and Classification of Enzymes Enzymes are classified according the report of a Nomenclature Committee appointed by the International Union of Biochemistry. This enzyme commission assigned each enzyme a systematic name and a code number , called enzyme commission ( EC) number . The systematic name contains two parts – the name(s) of substrate(s) involved and type of reaction catalyzed. Enzymes are also represented by a common name for simplicity .

11. Nomenclature and Classification of Enzymes The code numbers, prefixed by EC , which are now widely in use, contain four elements separated by points, with the following meaning: ( i ) the first number shows to which of the six main classes the enzyme belongs, (ii) the second figure indicates the subclass, (iii) the third figure gives the sub-subclass, (iv) the fourth figure is the serial number of the enzyme in its sub-subclass.

12. Nomenclature and Classification of Enzymes The enzyme commission ( EC ) numbers divides enzymes into six main classes according to the type of reaction catalysed . 1 . Oxidoreductases 2. Transferases 3. Hydrolases 4. Lyases 5. Isomerases 6. Ligases

13. Nomenclature and Classification of Enzymes Example: EC 1.1.1.1 refers to the enzyme alcohol dehydrogenase (common name ). Its systematic name is alcohol : NAD + oxido reductase . It catalyses the oxidation of alcohol to an aldehyde or ketone . Reaction: an alcohol + NAD + an aldehyde or ketone + NADH + H + First digit 1 indicates the major class oxidoreductase Second digit 1 indicates the subclass acting on CH-OH group of donors Third digit 1 indicates the sub-subclass NAD + as the electron acceptor Fourth digit 1 indicates the serial number of the enzyme alcohol dehydrogenase

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