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Objectives• Describe the chemical properties of enzymes:

eg. Active site, catalytic efficiency, specificity, cofactor,regulation, compartmentalisation.

• Explain the classification of enzymes

• Describe the kinetics of enzyme catalysis:

-. Michaelis Menten equation-. Lineweaver Burk transformation

References:

1. Rao, N.M. 2006. Medical Biochemistry. 2nd Ed.

New Age, Publisher.

2. Baynes, J.W. Dominiczak, M.H. 2005. MedicalBiochemistry. 2nd Ed. Elsevier Mosby.

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What is Enzyme ?• Catalyst

• Increase rate of chemical reactions without changing the equilibrium

• Enzymes different from other catalyst:

-. Specific : each enzyme eat different reaction

-. Greater catalytic power than other catalyst

-. Catalytic action can be regulated –

 to ensure rate

of product formed not in excess of amount needed

• Localization: organ, tissue, cellular, subcellular

• Holoenzyme = Apoenzyme + Cofactor

•

Reactant = Substrate• Classified in to 6 groups = type of reaction

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 Active Site

= three dimensional cleft created by side chain of several amino acid Amino acid from different regions in the linear sequence of enzyme, folded,

side chains close at the active side

 Amino acid is classified into 2 functional groups:

1. Binding residues

2. Catalytic residues

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- In an enzyme, a `binding site’ = an `active site’ 

- 4 types of binding of small molecule (red) to the binding site of

a protein (shaded)

Electrostatic Hydrophobic Hydrogen Bond Van Der Walls

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Enzyme Specificity

• 1. Substrate

• 2. Reaction

• 3. Group

• 4. Absolute group

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Effect enzymes on activation energy

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Reaction Profile 

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Examples of

Reaction Profile 

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Examples of

Reaction Profile

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Factors That Influence Reaction Rate

Under a specific set of conditions, every reaction has its own

characteristic rate, which depends upon the chemical nature of

the reactants.

Four factors can be controlled during the reaction:

1. Concentration - molecules must collide to react;

2. Physical state - molecules must mix to collide;

3. Temperature - molecules must collide with enough energy to react;

4. The use of a catalyst.

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Cascade Model : Type reaction of enzymes

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Effects of temperature

Each enzyme has an optimal temperature in which it can function

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Effects of pH

Each enzyme has an optimal pH in which it can function

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