Biochemistry Lecture Notes 2nd Grade - Enzymes PDF

BIOCHEMISTRY ,2nd grade , Lec. 2(Enzymes) By: Prof. Dr. Eaman A. AL-Rubaee  Enzymes Enzyme inhibitors , classification of enzymes and serum enzymes  Learning Objectives: By the end of the lecture, the student should be able to : Define enzym...

BIOCHEMISTRY ,2nd grade , Lec. 2(Enzymes) By: Prof. Dr. Eaman A. AL-Rubaee  Enzymes Enzyme inhibitors , classification of enzymes and serum enzymes  Learning Objectives: By the end of the lecture, the student should be able to : Define enzymes inhibitors. Explain the code number of enzyme. Explain the Classification of enzymes. Describe the use of enzymes in diagnosis.  Substrate Concentration and Reaction Rate The rate of reaction increases as substrate concentration increases (at constant enzyme concentration) Maximum activity occurs when the enzyme is saturated (when all enzymes are binding substrate)  Enzyme Kinetics - Inhibition Competitive Inhibition Noncompetitive Inhibition Uncompetitive Inhibition Irreversible Inhibition  Enzyme Inhibitors Competive - mimic substrate, may block active site, but may dislodge it.  Enzyme Inhibitors Noncompetitive  Naming Enzymes The name of an enzyme in many cases end in –ase For example, sucrase catalyzes the hydrolysis of sucrose The name describes the function of the enzyme For example, oxidases catalyze oxidation reactions Sometimes common names are used, particularly for the digestion enzymes such as pepsin and trypsin Some names describe both the substrate and the function For example, alcohol dehydrogenase oxides ethanol  Naming Enzymes The name of an enzyme in many cases end in –ase For example, sucrase catalyzes the hydrolysis of sucrose The name describes the function of the enzyme For example, oxidases catalyze oxidation reactions Sometimes common names are used, particularly for the digestion enzymes such as pepsin and trypsin Some names describe both the substrate and the function For example, alcohol dehydrogenase oxides ethanol  Principle of the international classification Each enzyme has classification number consisting of four digits: Example, EC: (2.7.1.1) HEXOKINASE  EC: (2.7.1.1) these components indicate the following groups of enzymes: 2. IS CLASS (TRANSFERASE) 7. IS SUBCLASS (TRANSFER OF PHOSPHATE) 1. IS SUB-SUB CLASS (ALCOHOL IS PHOSPHATE ACCEPTOR) 1. SPECIFIC NAME ATP,D-HEXOSE-6-PHOSPHOTRANSFERASE (Hexokinase)  6 CH2OH 6 CH OPO 2 2 3 ATP ADP 5 O 5 O H H H H H H 4 1 4 H 1 OH H OH Mg2+ OH OH OH OH 3 2 3 2 H OH Hexokinase H OH glucose glucose-6-phosphate 1. Hexokinase catalyzes: Glucose + ATP  glucose-6-P + ADP ENZYME NOMENCLATURE AND CLASSIFICATION NOMENCLATURE Each enzyme is assigned two names. The first is its short, recommended name, convenient for everyday use. The second is the more complete systematic name, which is used when an enzyme must be identified without ambiguity. A. Recommended name Most commonly used enzyme names have the suffix “-ase” attached to the substrate of the reaction (for example, glucosidase and urease), or to a description of the action performed (for example, lactate dehydrogenase and adenylyl cyclase). [Note: Some enzymes retain their original trivial names, which give no hint of the associated enzymatic reaction, for example, trypsin and pepsin.] B. Systematic name In the systematic naming system, enzymes are divided into six major classes (Figure 5.1), each with numerous subgroups. For a given enzyme, the suffix -ase is attached to a fairly complete description of the chemical reaction catalyzed, including the names of all the substrates; for example, lactate:NAD+ oxidoreductase. [Note: Each enzyme is also assigned a classification number.] 1- Oxidoreductases Oxidation-reduction reactions Glucose oxidase (EC 1.1.3.4) 2- Transferases Transfer of functional groups Hexokinase (EC 2.7.1.2) 3- Hydrolases Hydrolysis reactions Carboxipeptidase A (EC 3.4.17.1) 4- Lyases Addition to double bonds Pyruvate decarboxylase (EC 4.1.1.1) 5- Isomerases Isomerisation reactions Malate isomerase (EC 5.2.1.1) 6- Ligases Formation ob bonds (C-C, C-S, CO and C-N) with ATP cleavage Pyruvate carboxylase (EC 6.4.1.1)  Measurement of serum enzymes  Diagnostic enzymology  Enzymes are normally intracellular and LOW concentration in blood  Enzyme release (leakage)in the blood indicates cell damage (cell –death, hypoxia, intracellular toxicity)  Quantitative measure of cell/tissue damage  Fairly non invasive possible to do repeated tests Organ specificity- but not absolute specificity in spite of same gene content. Most enzymes are present in most cells-differing amounts Information from enzymes measurements in serum  Presence of disease  Organs involved  Aetiology /nature of disease: differential diagnosis  Extent of disease-more damaged cells-more leaked enzymes in blood  Time course of disease  Enzymes routinely measured NAME OF THE ENZYME PRESENT IN Aspartate Amino transferase (AST) Heart and Liver Serum glutamate-oxaloacetate transaminase (SGOT) Alanine Amino transferase (ALT) Heart and Liver Serum glutamate-pyruvate transaminase (SGPT) Alkaline Phosphatase (ALP) Bone, intestine and other tissues Acid Phosphatase (ACP) Prostate  glutamyl Transferase ( GT) Liver Creatine kinase (CK) Muscle Including cardiac muscle Lactate Dehydrogenase (LDH) Heart, liver, muscle, RBC  Amylase Pancreas  Isoenzymes catalyse same reactions but are formed from structurally different polypeptides. They perform the same catalytic function. Different isoenzymes may arise from different tissues and their specific detection may give clues to the site of pathology. Various isoenzymes of an enzyme can differ in three major ways: - enzymatic properties - physical properties (e.g heat stability) - biochemical properties such as amino acid composition and immunological reactivities.  Measurement of enzyme activity Enzyme activity is expressed in International unit (IU) It corresponds to the amount of enzymes that catalyzes the conversion of one micromole (mol) of substrate to product per minute  LACTATE DEHYDROGENASE (LDH) Pyruvate Lactate (anaerobic glycolysis)  LDH is elevated in myocardial infarction, blood disorders  It is a tetrameric protein and made of two types of subunits namely H = Heart, M = skeletal muscle  It exists as 5 different isoenzymes with various combinations of H and M subunits Isoenzyme Composition Composition Present in Elevated in name LDH1 ( H4) HHHH Myocardium, myocardial RBC infarction LDH2 (H3M1) HHHM Myocardium, RBC LDH3 (H2M2) HHMM Kidney, Skeletal muscle LDH4 (H1M3) HMMM Kidney, Skeletal muscle LDH5 (M4) MMMM Skeletal Skeletal muscle muscle, Liver and liver diseases  CREATINE KINASE (CK) Creatine + ATP phosphocreatine + ADP (Phosphocreatine – serves as energy reserve during muscle contraction)  Creatine kinase is a dimer made of 2 monomers occurs in the tissues  Skeletal muscle contains M subunit, Brain contains B subunits  Three different isoenzymes are formed Isoenzyme Composition Present in Elevated in name CK-1 BB Brain CNS diseases Acute Myocardium CK-2 MB myocardial / Heart infarction Skeletal CK-3 MM muscle, Myocardium