Enzymes are proteins - James Batcheller Sumner

Lock-Key Theory

• In 1894, German chemist Emil Fischer proposed the lock and key theory, which states that enzymes have a specific shape that directly correlates to the shape of the substrate. Basically, substrates fit into an enzyme the way a key fits into a lock.

Induced FIt Theory

• The induced-fit model was first proposed by Koshland in 1958 to explain the protein conformational changes in the binding process. This model suggests that an enzyme, when binding with its substrate, optimizes the interface through physical interactions to form the final complex structure.

Catalysts

• substances that speed up chemical reactions

• enzymes are specific for one particular reaction or group of related reactions

• many reactions cannot occur without the correct enzyme present

General Characteristics of Enzymes

Enzymes are well-suiter to their roles in three major ways:

• they have enormous catalytic power (or enzyme action)

• they are highly specific

  Degrees of specificity

  • Absolute - they are the only one who should be partnered (Lock and Key Theory)

  • Relative - it is within the family of a compound or substance

    • Toothpaste - relative

    • Toothbrush - absolute

  • Stereospecificity - depends on type of stereoisomer

• their activity can be regulated

Catalysis - also called enzyme action

Enzyme parts

Apoenzyme - a protein that forms an active enzyme system by combination with a coenzyme and determines the specificity of this system for a substrate.

Proenzyme or Zymogen - inactive enzyme that need activation (activates through activator)

Cofactor - inorganic helper of enzyme

Coenzyme - organic helper of enzyme

Enzyme nomenclature

Trivial System

• based on the substrate of the enzyme and the type of reaction catalyzed

• use of “-ase” ending

• substrate and reactant are same

International Enzyme Commission

• group of enzymes into 6 classes

Properties of Enzymes

• Enzymes are proteins - because of amino acids

• Enzymes are catalysts - cellular reactions must happen rapidly

• Enzymes are highly specific

Chemical Reactions

• All chemical reactions require an initial input of energy called activation of energy

• Reactions become more likely to happen if their activation energy is lowered

  • This process is called catalysis

  • Catalyzed reactions proceed must faster than non-catalyzed reactions

• Chemical reactions form new substance through activation

• Lower activation energy = longer process

How Enzymes Work

• enzyme-substrate complex

• enzymes bind specifically to a molecule and stress the bonds to make the reaction more likely to proceed

• active site is the site on the enzyme that binds to a reactant

• binding site is the site on the reactant where the enzyme binds

• The binding of the reactant to an enzyme causes the enzyme's shape to change slightly - leading to an "induced fit"

• the enzyme lowers the activation energy for the reaction

• the enzyme is unaffected by the chemical reaction and can be re-used

Mechanism of Enzyme Action

Allosteric site - where inhibitor attaches

presence of product can be a signal molecule

This can affects the process of enzymes

Competitive - it mimics the shape of substrate

Non-competitive - acts like repressor. It stops activity through alteration of active site.

How cells regulate enzymes?

Cells can control enzymes by altering their shape

• repressors - feedback inhibition

• activators

  Enzyme Inhibition