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