Introduction to model for enzyme action

Enzymes are complex biochemical catalysts, speeding up a particular reaction to produce an ordered, stable reaction system in which the products of any reaction are made when they are needed. A specific enzyme controls each reaction in a series of metabolic reactions. Enzymes also control cell metabolism by regulating how and when reactions occur.

They are made up of globular proteins that have complex tertiary or quaternary structure. Enzyme shape is maintained by hydrogen bonds and ionic forces and their function can be affected by changes in temperature and pH.

Model for Enzyme Action are Prepared Based on some Important Properties of Enzymes

• Each enzyme is specific and catalyzes only one reaction at a time
• Enzymes combine with their substrates to form temporary enzyme-substrate complex.
• Enzymes are not altered or used up in the reactions they catalyse, so can be used again and again.
• Enzyme catalysed reactions are sensitive to temperature and pH.
• Enzyme catalysed reactions can be slowed down or stopped by inhibitors.
• Enzymes lower the activation energy of a reaction thus making the reaction to occur very rapidly with large turnover numbers.

Model for Enzyme Action

There are two models proposed for enzyme action. They are as follows:

Lock and key model for enzyme action

It was proposed by Emil Fischer. Lock and key model states that a substrate fits into the enzyme in a similar way as a key fits into a specific lock. The active site is a particular shape (the lock) into which only one substrate (the key) will fit. The substrate fits the active site because it is a complementary shape and because the chemical charges attract each other (amino acids at active site are charged). The enzyme and substrate combine for an instant to form an enzyme substrate complex. The formation of this complex brings about the desired chemical reaction, converting substrate into products.

Induced fit model for enzyme action

It was proposed by Daniel Koshland. This model suggests that the active site in many enzymes is not exactly the same shape as the substrate, but moulds itself around the substrate as the enzyme substrate complex is formed. Before substrate binding the active site of the enzyme is relaxed. When the substrate binds the active site is pulled into correct shape by molecular interactions between the two molecules and an enzyme- substrate complex forms. As the products fall away from the active site, the molecule becomes relaxed again