Enzymes (1) 2.pdf

Professor: Yassir A. Almofti Dept: Biomedical Sciences Vet-Med KFU  A- Enzymes: history & definition  Enzyme, in Greek, means in living  (en= in zyme= living  Enzymes are biocatalyst or organic catalyst with high molecular weight (except RNA enzymes, Ribozymes).  The name enz...

Professor: Yassir A. Almofti Dept: Biomedical Sciences Vet-Med KFU  A- Enzymes: history & definition  Enzyme, in Greek, means in living  (en= in zyme= living  Enzymes are biocatalyst or organic catalyst with high molecular weight (except RNA enzymes, Ribozymes).  The name enzymes was coined by Kuhne in 1878 and the first enzyme was extracted from yeast by Buchner 1897.  The first purified enzyme was the Urease by James B. Summer in 1926 Definition  Enzymes are proteins (biological catalysts) that increase the rate of the reaction by lowering the activation energy  Enzymes catalyze nearly all the biochemical reactions in the cells of the body  Enzymes have unique three dimensional shape that fit the shape of the reactants What is the ACTIVATION ENERGY  It is the initial amount of energy need to start a chemical reaction and is often supplied in the form of heat from the surroundings  Think of the activation energy as the BARRIER required to make a product  The most stable product is the one with the lowest energy  Most reactions require a ‘PUSH’ to get them started  PUSH is called the activation energy Characteristics of Enzymes  Enzymes generally act quickly The speed of the reaction is based on the number of the substrates present  Enzymes are not damaged during the reaction This doesn’t mean enzymes can be used repeatedly for ever without replacement  Enzymes can react in both directions  Enzymes are specific Enzymes are limited to one specific reaction involved for specific substrate  The enzyme molecule is usually bigger than its substrate  All enzymes are protein and not all the proteins are enzymes  Enzymes are complex globular proteins with three dimensions B- Nomenclature & classification Trivial Names of Enzymes  The name of Enzymes usually end in-ase (Dehydrogenase)  Sometimes the name of the enzyme identifies the reacting substance Eg: Sucrase catalyzes the reactions of Sucrose  Sometimes describe the function of the enzyme Eg: Oxidases catalyze the oxidation  Could be a common name, particularly, for digestion enzymes Eg: pepsin and trypsin Systemic nomenclature  According to the International Union of Biochemistry (IUB) an enzyme has two parts: a. The first is the name of the substrate for the enzyme b. The second is the type of the reaction catalyzed by the enzyme. This part ends with the suffix ‘ase’ Example: Lactate dehydrogenase Pyruvate carboxylase IUB classification of enzymes Enzymes are classified according to the reaction they catalyze EC numbers: Enzyme commission numerical code EC numbers are four digits (a, b, c, d) a: the class of the enzyme (there are 6 classes) b: the functional group upon which the enzyme works (-OH, -CHO) c: the coenzyme Eg: NAD, FAD d: the substrate Example: Alcohol: NAD oxidoreductase EC number 1.1.1.1 EC (1): the class of the enzyme EC 1. (1): the functional group of the enzyme is CH-OH EC 1.1. (1):the coenzyme is NAD EC 1.1.1 (1): the substrate is Alcohol Eg: Ethanol C- Enzymes terminologies Enzymes: are proteins produced by the cells of living organisms and act as biological catalysts accelerating the biochemical reactions by lowering the activation energy Substrate: is the substance upon which the enzyme act in biochemical reaction Coenzymes: are small organic molecules that transport chemical groups (NAD, FAD) Cofactor: is non protein, heat stable, small MW substances and has the same function like Coenzymes (Mg+2 Fe+2 Cu+2) Ribozymes: (Ribonucleic acid enzymes) also called RNA enzymes. They are an RNA molecules the catalyze a chemical reaction by hydrolyzing one of their own phosphodiester bonds or the bonds in other RNAs Enzyme active site: is a region within the enzyme that fit the shape of the substrate Zymogen: are inactive form of enzymes (proenzymes) because the active site masked with polypeptide chain such as: Pepsinogen (inactive) Pepsin (active form) Trypsinogen (inactive) Trypsin (active form) Isoenzymes: are the enzymes that catalyze the same reaction in different tissues in the body Eg: lactate dehydrogenase enzyme has 5 isoenzymes  D- Mechanism of enzymes action  The proper fit of the substrate (S) in the active site of the enzyme (E) forms Enzy-Sub (ES) complex (E+S ES complex  Within the ES complex, the reaction occurs and converts the substrate (S) to a product (P): ES E+P  The product (P) which are no longer attracted by the active site, is released  The overall reaction is the conversion of the substrate to product E+S ES E+P  Induced fit model Lock and key model  The active site is flexible  The active site is rigid  The shape of the enzyme,  only substrates with the active site and the matching shape can fit substrate adjust to maximum the fit which  Only one substrate can fit improve catalysis to the active site  There is a greater range of substrates specificity  E- Factors affecting enzyme catalyzing reactions (1)Temperature and enzyme action  Enzymes are most active at optimum temperature (usually at 37C in humans)  Enzymes show little activity at low temperature  They lose activity at high temperature as denaturation occurs (2) pH and enzyme action  Enzymes are most active at the optimum pH  They lose activity in low or  high pH as tertiary structure  is disrupted (3)Enzyme (4)Substrate concentration concentration  The rate of reaction increases  The rate of reaction as enzyme concentration increases as Substrate increases (at constant concentration increases (at substrate concentration) constant enzyme  At higher enzyme concentration) concentrations, the more the  Maximum activity occurs substrate binds with enzyme when the enzyme is saturated  F- Enzymes inhibition  What is the inhibitor?  It is any substance that can diminish the velocity of an enzymatic reaction (can decrease or stop the enzyme action)  Enzyme inhibition can be classified as a. Competitive inhibition b. Noncompetitive inhibition (Allosteric inhibition) a. Competitive inhibition b. Noncompetitive inhibition  The inhibitor binds or The inhibitor binds to another competes with the substrate site in the enzyme called the in the active site of the allosteric site changing the enzyme structure of the active site