Enzyme Classification Properties and Kinetics PDF

ENZYME CLASSIFICATION AND THE SIX CLASSES NOMENCLATURE EC 1. Oxidoreductases EC 2. Transferases Trivial name EC 3. Hydrolases...

ENZYME CLASSIFICATION AND THE SIX CLASSES NOMENCLATURE EC 1. Oxidoreductases EC 2. Transferases Trivial name EC 3. Hydrolases Gives no idea of source, function or reaction EC 4. Lyases catalyzed by the enzyme. EC 5. Isomerases Example: trypsin, thrombin, pepsin. EC 6. Ligases Nomenclature and Classification EC 1. OXIDOREDUCTASES Nomenclature - system of naming organisms - catalyze the transfer of hydrogen or oxygen Classification - is arranging them in groups atoms or electrons from one substrate to according to their similarity or differences. another, also called oxidases dehydrogenases, or reductases. Note that Systematic Name since these are 'redox' reactions, an electron According to the International union of donor/acceptor is also required to complete Biochemistry an enzyme name has two the reaction. parts: EC 2. TRANSFERASES - First part is the name of the substrates for the - catalyze group transfer reactions, excluding enzyme. oxidoreductases (which transfer hydrogen or oxygen and are EC 1). These are of the - Second part is the type of reaction catalyzed general form: by the enzyme. This part ends with the suffix A - X +B ↔ BX+A "ase". EC 3. HYDROLASES Example: Lactate dehydrogenase - catalyze hydrolytic reactions. Includes lipases, esterases, nitrilases, peptidases/proteases. EC number These are of the general form: Enzymes are classified into six different A-X + H2O ↔ Х-ОН + НА groups according to the reaction being catalyzed. EC 4. LYASES - catalyze non-hydrolytic The nomenclature was determined by the (covered in EC 3) removal of functional groups Enzyme Commission in 1961 (with the latest from substrates, often 2. Enzymes are not update having occurred in 1992), hence all used up in the reaction they catalyse they can enzymes are assigned an "EC" number! be used again and again. Creating a double bond in the product; or the reverse reaction The classification does not take into account i.e., addition of function groups across a amino acid sequence (ie, homology), protein double bond structure, or chemical mechanism. A-B → A = B+X-Y XY EC numbers are four digits, for example Includes decarboxylases and aldolases in the a.b.c.d, where "a" is the class, "b" is the removal direction, and synthases in the addition subclass, "c" is the sub-subclass, and "d" is direction. the sub-sub-subclass. The "b" and "c" digits describe the reaction, while the "d" digit is EC 5. ISOMERASES used to distinguish between different - catalyzes isomerization reactions, including enzymes of the same function based on the racemizations and cis- tran isomerizations. actual substrate in the reaction. EC 6. LIGASES Example: for Alcohol: NAD+oxidoreductase EC - catalyzes the synthesis of various (mostly C- number is 1.1.1.1 X) bonds, coupled with the breakdown of energy containing substrates, usually ATP  PROPERTIES OF ENZYMES 5. Enzymes are fast acting i.e.; they have a high turnover number. They can convert many 1. High degree of specificity for their substrates. molecules of substrate per unit time. Each enzyme will catalyse only one particular reaction. 2. Enzymes are not used up in the reaction they catalyse; they can be used again and again. 6. Enzymes are affected by changes in temperature and pH. 3. When enzymes react they combine with substrates to form ES complexes 7. Many enzymes work only if a chemical called cofactor is present 4. Only small amount of enzy me is needed to catalyse a lot of substrate 8. Enzyme catalysed reactions are slowed down or stopped by inhibitors  FUNCTIONS OF ENZYMES Enzyme (as a catalyst) acts on substrate in such a way that they lower the activation Role Of Enzymes in The Body energy by changing the route of the reaction. 1. DEGRADATION REACTIONS (CATABOLIC) 2. SYNTHESIS (ANABOLIC) The reduction of activation energy (Ea) 3. DIGESTION increases the amount of reactant molecules - Enzymes are used for a wide variety of that achieve a sufficient level of energy, so that purposes, such as in digestion. they reach the activation energy and form the 4. PROTECTION product. - Enzymes are also used in protection against Pathogens. They can be used to Example: destroy invading Microorganisms. Carbonic anhydrase catalyses the hydration of 10° CO₂ molecules per second which is 10'x faster than spontaneous hydration. KINETICS OF ENZYMES CATALYSIS Enzymes catalysis: KINETICS "It is an increase in the rate of reaction with the help of enzyme (as catalyst)." INTRODUCTION Catalysis by enzymes that proceed via unique "It is a branch of biochemistry in which we study reaction mechanism, typically occurs when the the rate of enzyme catalyzed reactions." transition state intermediate forms a covalent bond with the enzyme (covalent catalysis). Kinetic analysis reveals the number and order of the individual steps by which enzymes During the process of catalysis enzymes transform substrate into products always emerge unchanged at the completion of the reaction. Studying an enzyme's kinetics in this way can reveal the catalytic mechanism of that enzyme, its role in metabolism, how its activity is controlled, and how a drug or an agonist might inhibit the enzyme RATES OF REACTION AND THEIR DEPENDENCE ON ACTIVATION ENERGY Activation Energy (Ea); "The least amount of energy needed for a chemical reaction to take place."