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Enzymes-2 – Properties, classification and theories of action lecture NO : 1st MBBs Dr Muhammad Ramzan Properties – the definition • Any measureable aspect of the system that is essential to maintain the material structure of life • The property can Physical like size shape and : • Chemical like nature of the molecule Protein CHO, Lipids and Nucleic acid The properties of enzymes • • • • • • • Followings are the enzymes‘ properties The nature . Activation energy and Active site Catalytic efficiency and Enzyme specificity Regulation of enzyme activity Distribution/location of enzyme Site of synthesis and action Nature of the Enzymes • All the enzymes are proteins that ↑ the velocity of a chemical reaction and are not consumed during the reaction • Some of the RNAs also act as enzymes like rRNAs- Ribozymes that are involved in protein synthesis • These RNAs establish peptide bond B/W the Amino acids of the Product proteins Activation energy • It is the minimum amount of energy required to Initiate and complete a catalyzed chemical reaction • Enzymes reduce the activation energy to make the reactants • (Enzyme and Substrate) to bind for ESC : • and transformed into Products • It is much lower than required for the non catalyzed reactions Active site – Has functional/Amino Acyl groups (2-4 AAs) • • • • • Active sites are the pockets/hollows on the surface of E that assumes 3D shape after protein folding Active site contains the side chains of the AAs (amino Acyl or functional groups 2 - 5 AAs) that are involved in the : Substrate binding and Catalysis Binding of S to active site produces ESC which is cleaved to products and enzyme . Both are released and enzyme can be reused Active site Catalytic efficiency • Es are the efficient catalysts and can ↑ the rate of chemical reaction up to 103 to 108 than the uncatalysed reaction • About 100 to 1000 substrates are transformed into the products / unit time • Turnover number is the maximum no: of substrates converted into products/ active site/ unit time • Turn over no: of Carbonic Anhydrase is 36million/active site/minute Enzyme specificity • Enzymes are highly specific and interact with specific substrates with specific functional groups • Other substrates would not fit into their active sites • It catalyzes only one type of chemical reaction • The set of enzymes present in a cell determines which type of reaction will occur in that cell Cofactors - property of enzymes non protein parts of E • Cofactors are the non protein components of an enzyme and is essential for E activity • Halozyme is an active enzyme with protein and a cofactor • There are 2 types of cofactors that bind to the active site • Inorganic metallic ions : like Iron, Magnesium and Zinc. • Also called as Co factors 1 • Organic molecules: like Co A; NAD,NADH and FAD • Also called as Coenzymes 2 Regulation of enzyme activity • Enzyme activity can be regulated • Cell regulates the activity of the enzyme according to their demand and need through E activation or inhibition • Like Glycogen Synthase is active when there is excess of glucose and body needs to store CHOs as Glycogen • Its activity is inhibited when there is hypoglycemia Distribution/Location of enzymes 1 Intra/Extra cellular • Majority of the E are intracellular except digestive enzymes which are present in the lumen of GIT • Enzymes are also localized in the specific organelles called compartmentalization like Mitochondria that : • House the enzymes for FA oxidation and Citric acid cycle • Intra cellular Es are secreted in small and Extra cellar in large quantities Location of enzymes 2 • Cytosole has the enzymes for Glycolysis, Fatty acid synthesis and HMP pathway • Lysosomes contain the enzymes (Hydrolases) for the : • Degradation of macromolecules like TG; Proteins, Glycogen and Nucleic acids • Compartmentalization provides the favorable environment for the reactions to occur Site of synthesis/action reused and measured • The site of synthesis and action is the same • A small amount of E is required for catalysis • Enzymes can be reused and measured for diagnostic and monitoring (treatment) purposes Classification of enzyme – by adding suffix - "ase" • Es are commonly named by adding the suffix "-ase" to the root name of the substrate molecule it is acting upon. • For example, Lipase catalyzes the hydrolysis of lipids/TG • Sucrase catalyzes the sucrose into Glucose and fructose • A few enzymes discovered before this naming system are known by their common names • Examples are the Pepsin and Trypsin which catalyze the proteins .AAs Classification of enzymes – IEC Based upon type of reaction • The latest systematic nomenclature system known as the International Enzyme Commission (IEC) system • is based upon the type of reaction catalyzed. • There are six broad groups of enzymes in this system Classification of enzymes - Reaction types Enzyme action – theories or Models Active site is common to all E • Enzymes differ widely in structure and specificity, but a general theory that accounts for their catalytic behavior • is widely accepted. Like : • The enzyme and its substrates interact only over a small region over the surface of the enzyme • called the Active site. Theories /models of enzyme action. 3 • • • • • There are 3 theories about mechanism of E action with minor difference of the flexibility or rigidity of the Active site and changes in the conformation/shape of : Enzyme, substrate and active site Lock and key Theory Induced – fit theory The Transition – State Model/Theory Lock and key theory • The lock-and-key theory explains the high specificity of E activity. - Enzyme surfaces accommodate substrates, having specific shapes , sizes and functional groups – So only specific substances ― fit in an active site to form • a ES complex. Limitation of Lock and key theory Rigid E conformation • A limitation of this theory is that it requires enzymes • conformations to be rigid and so is the (active site) • Research suggests that enzymes conformations are not so rigid but some what flexible. Enzyme – Lock and key model Induced fit model/theory E/active site changes to S • This model is the more accepted for enzyme-substrate complex than the lock-and-key model. • It shows that enzymes are rather flexible structures in which the active site continually reshapes by: • Its interaction with the substrate until the substrate is completely bound to it. • Which is also the point at which the final form and shape of the enzyme is determined. Enzyme – Induced – fit model Transition- state Theory - TST S to activated Complex • Transition state theory begins with binding of the Substrate to the active site of the enzyme • There is a change in the Geometry of the S after E binding to assume a state that is neither a product nor ESC • This transition/activated complex undergoes catalysis to products • The demerit is the high cast of energy Transition state Model/Theory -TST Transition state/activated state theory