Section B- Drug targets B1 ENZYMES Key Notes Enzymes Enzymes are proteins that catalyze the body s chemical reactions. The starting material for an enzyme-catalyzed reaction is known as a Active site The active site is a hollow or cleft on the enzyme surface where the substrate binds and the reaction takes place. The substrate is bound to the active site by intermolecular interactions. The active site contains amino acid residues, which act as nucleophiles or acid/ base catalysts in the reaction mechanism Mechanisms of Serine and cysteine can act as nucleophiles in a reaction mechanism, catalysis while histidine can act as an acid/base catalyst Substrate binding weakens important bonds and constrains the substrate in a specific nformation such that it will undergo reaction Enuyme inhibitors Competitive inhibitors compete with the naturai substrate for the active site. Noncompetitive inhibitors bind to allosteric binding sites and distort he active site so that it can no longer bind the natural substrate Reversible inhibitors bind by noncovalent interactions, whereas irreversible inhibitors are linked to the enzyme through covalent bonds Enayme selectivity Drugs should be as selective as possible for the target enzyme Related topics inding interactions( G2) Modeling studies(L4) Functional groups as binding The dawn of the antibacterial ag groups( G3) (1930-1945)(M4) Epidermal growth factor receptor L1) Enzymes are protein structures that act as the body s catalysts. a catalyst aids a chemical reaction by lowering the activation energy of the reaction. This speeds up the rate at which the reaction reaches equilibrium but does not affect the equilibrium itself. Therefore, an enzyme can catalyze a reaction in either direc- tion depending on the relative ratio of compounds present. The chemical that undergoes an enzyme-catalyzed reaction is known as a substrate. The substrate is bound to the enzyme to form an enzyme-substrate complex (ES), which then undergoes reaction to form the enzyme- bound product(EP)(Fig. 1).The product is then released and the enzyme is free to bind another substrate Since enzymes are proteins, they are made up of amino acid subunits linked together by peptide bonds. There are 20 essential amino acids in human biochemistry five of which are shown in Fig.2