CHEMISTRY OF ENZYMES

DEFINITION

Enzymes are protein catalysts that increase the rate of reaction without being changed in the overall process.

CHARACTERISTICS OF ENZYMES1. Almost all enzymes are PROTEIN2. Heat labile.3. Water soluble.4. Precipitated by protein precipitating reagents.5. Contain 16% weight as nitrogen.

CHEMICAL NATURE OF ENZYMES APOENZYME Protein component of enzyme. HOLOENZYME Apoenzyme + non protein component. CO ENZYME Non protein organic/ metallo organic molecules;

non covalently/covalently(prosthetic group) attached to the enzyme.

CHEMICAL NATURE OF ENZYMES CO FACTORS Inorganic / metallic ions forming a loose, easily

dissociable complex.

PROSTHETIC GROUP Co factors /co enzymes that are tightly bound to

the enzyme.

TERMINOLOGY

SUBSTRATEThe substance upon which an enzyme acts is called the substrate.TURNOVER RATEThe number of substrate molecules acted upon by an enzyme in

one second under appropriate conditions.INTERNATIONAL UNITAmount of enzyme causing Transformation of 1µmol of

substrate/minute under optimal conditions.

ACTIVITYTotal units of enzymes in a given solution.

SPECIFIC ACTIVITYNumber of enzyme units/mg of total protein.

KATALAmount of an enzyme which catalyzes a reaction rate of 1

mole of substrate/second.

TERMINOLOGY

ACTIVE SITE Special pocket or cleft in an enzyme molecule. Has amino acid side chains for substrate binding

& catalysis. ALLOSTERIC SITES Enzymes have allosteric sites(other than active

site) where effectors (chemical reagents acting as modifiers) bind through non covalent linkage.

TERMINOLOGY

E-S COMPLEX THEORIES

FISCHER΄S TEMPLATE THEORY

KOSHLAND΄S INDUCED FIT THEORY

FISCHER΄S TEMPLATE THEORY

FISCHER΄S TEMPLATE THEORY

KOSHLAND΄S INDUCED FIT THEORY

Enzyme catalyzed reactions have three basic steps;

Binding of substrate E + S ES Conversion of bound substrate to bound

product ES EP Release of product EP E + P

MECHANISM OF ENZYME ACTION

ENERGY CHANGES

CHEMICAL CATALYSIS

ENERGY CHANGES All chemical reactions have an energy barrier

separating the reactants & the products; called free energy

of activation--- E –act.

ENERGY OF ACTIVATION Energy required to convert all molecules of a

reacting substance from the ground state to the transition state.

TRANSITION STATE High energy intermediates state during the

conversion of reactants & the products. A T * B Enzymes greatly decrease the E-act & stabilize

the transition state. RATE OF REACTIONRate of reaction is ¹/α to the E-act.> The E-act < the reaction rate.

TRANSITION STATE STABILIZATION

CHEMICAL CATALYSISCatalysis by proximityAcid base catalysisCatalysis by strainCovalent catalysis

CATALYSIS BY PROXIMITY For molecules to react, they must come within

bond forming distance of one another. When enzyme binds substrate molecule at its

active site, it creates a region of high local substrate concentration.

Orients substrate molecules spatially in a position ideal for them to interact, resulting in rate enhancement .

ACID BASE CATALYSIS Ionizable functional groups of amino acid side

chains & of prosthetic groups act as acids or bases.

CATALYSIS BY STRAIN Enzymes that catalyze lytic reaction ,involve in

breaking of a covalent bond , bind their substrate in a conformation that induces strain in the substrate , converting it into transition state.

COVALENT CATALYSISCommon among enzymes that catalyze group transfer reaction.Formation of covalent bond b/w enzyme & one or more substrate.Covalent catalysis ↓ the E-act & ↑ the reaction rate.Involves ping – pong mechanism.

PING – PONG MECHANISM