Enzyme Lecture PDF

▪ Enzymes: the biocatalysts mainly proteins in nature that regulate rate of all biochemical reactions. ▪ Substrate: The substance on which enzyme acts. ▪ Product: The substance produced by the action of enzyme on the substrate. ▪ The active site: a special pocket or cleft on enzyme surface. It conta...

▪ Enzymes: the biocatalysts mainly proteins in nature that regulate rate of all biochemical reactions. ▪ Substrate: The substance on which enzyme acts. ▪ Product: The substance produced by the action of enzyme on the substrate. ▪ The active site: a special pocket or cleft on enzyme surface. It contains amino acid side chains that create a three-dimensional surface complementary to the substrate. All are protein in nature All are produced by living cells and can act outside these cells They are needed in very small amounts Common features and properties They are not changed chemically by the end of the reaction They accelerate the reaction without affecting its equilibrium (decrease energy of activation) They are highly specific (act on a specific substrate) Common features and properties Enzyme Nomenclature The suffix ase to the name of the substrate e.g. maltase, lactase, sucrose. (trivial naming of the enzymes) to a description of the action performed e.g. lactate dehydrogenase, pyruvate carboxylase. old name which give no hint of the associated enzymatic reaction e.g. trypsin,pepsin. ▪ six major classes each with numerous subgroups (according to their main function) Class of enzyme Reaction catalyzed Oxidoreductases Oxidation-Reduction reactions Transferases Transfer of functional groups Hydrolases Hydrolysis reactions Lyases Group elimination to form double bonds Isomerases Isomerization reactions Ligases Bond formation coupled with ATP hydrolysis Class of enzyme Reaction catalyzed Oxidoreductases Oxidation-Reduction reactions Transferases Transfer of functional groups Hydrolases Hydrolysis reactions Lyases Group elimination to form double bonds Isomerases Isomerization reactions Ligases Bond formation coupled with ATP hydrolysis Holoenzyme Apoenzyme (Protein part) Non-protein part Tightly bound (Prothetic group) Loosely bound Cofactor Coenzyme ▪These are group of enzymes which are attached together and catalyze a certain reaction ▪They affect the substrate in sequential manner so that the product of the first enzyme will be the substrate of the second one until formation of the final product. e.g. Pyruvate dehydrogenase complex. Enzymes in clinical diagnosis 1- Enzymes may be measured in cells to detect enzyme deficiency in certain diseases e.g. deficiency of red cell G6PD in favism. 2- Measuring the level of certain enzymes in blood plasma helps the diagnosis of many diseases e.g.: high levels of CK (CK-MB), LDH and aspartate aminotransferase (AST) are specific for myocardial infarction. Plasma enzymes may be functional, which are enzymes that perform a certain function in the blood, or nonfunctional. These are a group of enzymes which are characterized by the following: ▪ They catalyze the same reaction. ▪ They have different polypeptide chains which are produced by different genes. ▪ They are separated by electrophoresis (have different migration rate). ▪ They have different affinity to the substrate. ▪ They are usually affected in different ways by the different activators and inhibitors. ▪ They are present in the same or different cells. Creatine Kinase Creatine Kinase (CK) or Creatine Phosphokinase (CPK): *CK BB (in brain) *CK MB (in heart) *CKMM (in muscle) Clinical significance of enzymes 1- Biochemical reactions 2- Diagnosis of diseases Extracted and purified enzymes Medical applications Enzymes are used in detergents and washing soaps Industrial applications Amylase, lactases, cellulases are enzymes used to break complex sugars Pectinase act on hard pectin in fruit juice manufacture