Biochemistry: A Short Course Second Edition

Tymoczko Berg Stryer

2013 W. H. Freeman and Company

CHAPTER 6 Basic Concepts of Enzyme Action

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Outline

6.1 Enzymes Are Powerful and Highly Specic Catalysts

6.2 Many Enzymes Require Cofactors for AcDvity

6.3 Free Energy Is a Useful Thermodynamic FuncDon for Understanding Enzymes

6.4 Enzymes Facilitate the FormaDon of the TransiDon State

CHAPTER 6 Basic Concepts of Enzyme Action

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Enzymes

have

specific

substrates:

trypsin

K or R^

thrombin

LVPR^GS

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1. Oxidoreductase catalyze oxida4on-reduc4on reac4ons.

2. Transferases move func4onal groups between molecules.

3. Hydrolyases cleave bonds with the addi4on of water.

4. Lyases remove atoms to form double bonds or add atoms to double bonds.

5. Isomerases move func4onal groups within a molecule.

6. Ligases join two molecules at the expense of ATP.

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For the reac4on:

The free energy change is given by:

Where Go is the standard free energy, R is the gas constant, T is 298 kelvins, and the brackets denote concentra4on in moles.

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Enzymes accelerate the reaction rate, but will not alter the reaction equilibrium 10

Enzymes accelerate reactions by decreasing

G, the free energy of activation.

Enzymes cannot alter this Grxn

ac4va4on energy

Can enzymes make a non-spontaneous rxn occur?

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Enzymes bring substrates together to form an enzyme-substrate complex on a par4cular region of the enzyme called the ac4ve site.

The interac4on of the enzyme and substrates at the ac4ve site promotes the forma4on of the transi4on state.

Active sites may include distant residues

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1. The ac4ve site is a three-dimensional cleV or crevice created by amino acids from dierent parts of the primary structure.

2. The ac4ve site cons4tutes a small por4on of the enzyme volume. 3. Ac4ve sites create unique microenvironments. 4. The interac4on of the enzyme and substrate at the ac4ve site involves

mul4ple weak interac4ons. 5. Enzyme specicity depends on the molecular architecture at the ac4ve

site.

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Lock-and-key model

Induced-fit model

Two models of enzymesubstrate binding:

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proline racemase

inhibitor

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