Enzyme Properties & Importance Lecture Notes PDF

21 Enzyme properties & their importance: ILOs By the end of this lecture, students will be able to 1. Describe the nature and properties of enzymes 2. Explain the importance of enzymes in metabolic reactions ❖ What are “Enzymes”? Enzymes are protein catalysts for chemical reaction in...

21 Enzyme properties & their importance: ILOs By the end of this lecture, students will be able to 1. Describe the nature and properties of enzymes 2. Explain the importance of enzymes in metabolic reactions ❖ What are “Enzymes”? Enzymes are protein catalysts for chemical reaction in biological systems. They increase the rate of chemical reactions taking place within living cells without being changed or consumed. ❖ Why are Enzymes important in the human body? Many reactions required for the living cell would not proceed fast enough at the pH and temperature of the body without enzymes. All the cellular reactions have high energy barrier (high energy needed by the reaction to take place) and proceed too slowly. Enzymes lower the energy barrier of these reactions required for cell survival therefore it increases the rate of the reaction without changing the reaction itself. Unwanted reactions would never occur spontaneously because of high energy barrier. ❖ What is the Nature of these “Enzymes”? 1. Simple enzyme: It is made up of only protein molecules not bound to any non-proteins. As Pancreatic Ribonuclease enzyme. 2. Holo enzyme is made up of protein groups and non-protein component. - The protein component of this holo enzymes is called apoenzyme - If the non-protein component of the holo enzyme is an organic compound it is called a coenzyme. - If the non-protein component of the holo enzyme is an inorganic group it is called cofactor. (Fe 2+, Mn 2+, or Zn 2+ ions). If the non-protein part is bound so tightly to the apoenzyme and is difficult to remove without damaging the enzyme it is sometimes called a prosthetic group ❖ Important Definitions: Isoenzymes (Isozymes) These are enzymes having similar catalytic activity, act on the same substrate and produce the same product but originated at different site and exhibiting different physical and chemical characteristics such as amino acid composition and immunological behavior. Example: LDH (Lactate dehydrogenase) exists in five different forms each having four polypeptide chains. H= Heart and M=Muscle. LDH-1 H H H H LDH-2 H H H M LDH-3 H H M M LDH-4 H M M M LDH-5 M M M M Page 1 of 3  ____________ Rate Limiting Steps The rate limiting step in any reaction is its slowest step. It sets the pace for the entire reaction. It usually occurs early in the pathway. After all, a production line can only be as productive as its slowest worker. Therefore the rate of the entire enzymatic reaction depends on the rate of this reaction. ❖ What are the main properties of Enzymes? 1- Active site Enzyme molecules contain a special pocket or cleft called the active site. The active site, formed by folding of the protein, contains amino acid side chains that participate in substrate binding and catalysis. The substrate (The molecule or reactant that the enzyme acts upon to form products) binds the enzyme non-covalently, forming an enzyme–substrate (ES) complex, where the substrate attaches itself to the specific active sites on the enzyme molecule by reversible interactions formed by Hydrogen bonds and Hydrophobic interactions. ES is then converted to an enzyme–product (EP) complex that subsequently dissociates to enzyme and product. How does the substrate bind to the enzyme? The enzyme substrate binding is no longer viewed as the rigid picture of a key lock binding, a more flexible model of the binding is provided by the “induced-fit model” in which the binding and active sites are not fully pre-shaped. The essential elements of the binding site are present to the extent that the correct substrate can position itself properly. Interaction of substrate with enzyme induces a conformational change in the enzyme, resulting in the formation of a stronger binding site and the repositioning of the appropriate amino acids to form the active site. Figure (5-1): Induced fit Model Page 2 of 3  2- Efficiency Most enzyme- catalyzed reactions are highly efficient proceeding from 10 3 to 108 times faster than uncatalyzed reactions. Typically each enzyme molecule is capable of transforming 100 to 1000 substrate molecule into product each second. 3- Specificity Enzymes are highly specific, interacting with one or a few substrates and catalyzing only one type of chemical reaction. Specificity of enzymes include: - Absolute specificity:- this means one enzyme catalyzes or acts on only one substrate. For example: Glutamate Dehydrogenase will catalyze only the removal of the nitrogen group from glutamate- NOT any other amino acid. - Bond Specificity: Enzymes that are specific for a bond or linkage such as Esterases- acts on ester bonds, Peptidases-acts on peptide bonds, Glycosidases- acts on glycosidic bonds. 4- Regulation Enzyme activity can be regulated, that is, increased or decreased, so that the rate of product formation responds to cellular need. This tight regulation helps in controlling several metabolic functions as the storage and release of energy and maintaining blood glucose levels in fed and fasting states, Digestion and absorption of nutrients, also the formation of complex molecules from the small, simple ones to produce cellular constituents 5- Location within the cell Many enzymes are localized in specific organelles within the cell. Such compartmentalization serves to isolate the reaction substrate or product from other competing reactions. This provides a favorable environment for the reaction and organizes the thousands of enzymes present in the cell into purposeful pathways. Page 3 of 3