EnzymesDefinitionClassificationChemistryPropertiesMechanism of enzyme actionFactors affecting enzyme activity

DefinitionEnzymes are biocatalyst that speeds up

digestion and metabolism.They are located in the cells, cytoplasm,

mitochondria, tissues and body fluids.EndoenzymesEnzymes that function within the cells. Most

of the enzymes are these types. Eg. metabolic enzymes (cytochrome oxidase)

ExoenzymesEnzymes that are liberated by cells and

catalyse reactions outside the cell. Eg. digestive enzymes (amylase, lipase, protease)

ClassificationEnzymes are named based on the substrate,

reaction, synthesis, chemical natureBased on the substrate:Enzymes are named by adding suffix-ase to

the name of substrateCarbohydrates carbohydrasesProtein proteinaseLipids lipasesNucleic acids nucleasesMaltose maltaseLactose lactaseSucrose sucraseUrea urease

Based on Enzyme Commission of the International Union of Biochemistry, enzymes are classified into six major classes.

Class Reactions catalyzedOxidoreductoases Oxidation-reductionTransferase Transfer group of

atomsHydrolases HydrolysisLyases Add/remove atoms

to/from a double bondIsomerases Rearrange atomsLigases Combine molecules using ATP

Chemistry of enzymesEnzymes are specialized large protein molecules

made of one or more polypeptide chains.Enzymes may be composed of only protein or

combination of protein and non protein part.Simple enzymes composed of only protein.Holoenzymes/conjugated comprise of protein

and non protein part.Protein component - apoenzymeNon protein part - co-factorProsthetic group - co-factor firmly attached to

enzymeCo-enzyme – co-factor loosely attached to

enzyme

Properties of EnzymesProteineous Accelerate chemical reaction without

itself undergoing changeSpecific in actionRequired in small quantityUndergoes denaturationReversibility of enzyme action

Mechanism of enzyme actionMichaelis and Menton proposed a

hypothesis for enzyme action.According to their hypothesis, the following

steps occurs: 1. combination of enzyme with substrate -substrate attaches on the active site of

enzyme to form enzyme-substrate complex.2. Breakdown of substrate -active site loosens the chemical bonds in

the substrate breaking down the substrate into products.

3. Dissociation of enzyme -enzyme finally dissociates from end

products and is free to combine another molecule of

substrate.

Formation of enzyme-substrate complex

Two hypothesis1. Lock and key hypothesis2. induced fit hypothesis

Lock and Key hypothesisProposed by Emil Fisher (1914)According to this hypothesis, the active

sites of enzyme are rigid with proper conformation.

The substrate simply fits into the active site to form a reaction intermediate.

Induced fit hypothesis

Proposed by Khosland (1963)According to this hypothesis, the active sites

are flexible.The enzyme molecule changes shape as the

substrate molecules gets closeThe substrate changes the conformation of

the active site of enzyme closely fitting on it.

Induced fit hypothesis

Factors affecting enzyme activity

The activity of enzyme is affected by a number of factors.

TemperatureEnzymatic activity increases with increase

in temp upto 40⁰C.Most of the enzyme the optimum temp