Enzymes-1 Lecture Notes PDF

International University of Africa Faculty of Medicine Department of Biochemistry Biochemistry – 1 Enzymes-1 By Dr. Mohammed Abdelrheem 5/10/2024 1  Enzymes Definition  Literal definition: in yeast.  Biochemical de...

International University of Africa Faculty of Medicine Department of Biochemistry Biochemistry – 1 Enzymes-1 By Dr. Mohammed Abdelrheem 5/10/2024 1  Enzymes Definition  Literal definition: in yeast.  Biochemical definition: They are proteins that act as catalysts (increase the rate of chemical reactions). 5/10/2024 2 The chemical nature of enzymes: Enzymes are proteins. Some enzymes are ribonucleic acids in nature. General features of enzymes: 1. Highly efficient: Gives 103-108 product per second. Act at 37°C. Don’t consumed or changed during the chemical reaction. 5/10/2024 4 Enzymes Characteristics  2. Specificity:  Substrate specificity:  Absolute specificity: enzyme attach one substrate only (urease for urea), and if the substrate is isomer (D or L isomer) the enzyme will work on only one isomer (stereospecificity). 5/10/2024 5   Group specificity: enzyme attack group of similar compounds (L-amino acid oxidase attack L-amino acids, but not D-amino acids).  Low or relative specificity: enzyme attach specific type of bonds (peptidase attack peptide bonds of different peptide proteins). 5/10/2024 6  Reaction specificity: e.g. glucose oxidase catalyse the pathway of gluconic acid synthesis, but not the synthesis of sorbitol.  Most enzymes names end with ase. 5/10/2024 7  Definition of Terms  Active site (often located in a cleft): is the substrate binding site.  Substrate of the enzyme: e.g. starch is the substrate of amylase, lipids is the substrate of lipase.  Holoenzyme (active enzyme) = Apoenzyme (protein part of enzyme) + Coenzyme or cofactor (non protein part of the enzyme). 5/10/2024 8 5/10/2024 9  Not all enzymes require coenzymes.  Coenzymes are complex nonprotein organic molecules of low molecular weight, function as group transfer reagents, and classified into two group: 5/10/2024 10  Prosthetic group (binds strongly with apoenzyme): e.g. heme in hemoglobin.  Cofactors (weekly bind, and easily dissociated from the apoenzyme): e.g. NAD in liver alcohol dehydrogenase. 5/10/2024 11  Not all enzymes synthesized active (zymogens): e.g. the digestive enzymes; pepsinogen, trypsinogen, and chemotrypsinogen.  Almost all of the polar amino acids participate directly in catalysis in one or more enzymes. 5/10/2024 12  Enzyme-Catalyzed Reaction (Michaelis-Menten Equation)  Have three steps: (1) Binding of substrate: E + S ES (2) Conversion of bound substrate to bound product: ES EP (3) Release of product : EP E+P 5/10/2024 13 5/10/2024 14 5/10/2024 15 Structure of enzyme: Active enzyme = protein part + non protein part Holo enzyme (apoenzyme) (cofactor) 5/10/2024 16 Protein part : Active site (Like a pocket or cleft) The role of active site : Binding of substrate Catalytic role of the enzyme Determine the specificity of enzyme The nomenclature of enzymes: Trivial names eg: pepsin ,trypsin Systematic names : Name of substrate + ase eg: lipase ,amylase ,protease Name of substrate + type of reaction + ase eg:Lactate dehydrogenase  THANKS 5/10/2024 21