Introduction to Enzymes

Enzyme Kinetics: The Enzyme Substrate Complex

A theory to explain the catalytic action of enzymes was proposed by the Swedish chemist Savante Arrhenius in 1888. He proposed that the substrate and enzyme formed some intermediate substance which is known as the enzyme substrate complex. The reaction can be represented as:

S + E → ES  [2]

S = Substrate; E = Enzyme; ES = Enzyme/Substrate Complex

If this reaction is combined with the original reaction equation [1], the following results:

S + E → ES → P+ E  [3]

S = Substrate; E = Enzyme; ES = Enzyme/Substrate Complex; P = Product

The existence of an intermediate enzyme-substrate complex has been demonstrated in the laboratory, for example, using catalase and a hydrogen peroxide derivative. At Yale University, Kurt G. Stern observed spectral shifts in catalase as the reaction it catalyzed proceeded. This experimental evidence indicates that the enzyme first unites in some way with the substrate and then returns to its original form after the reaction is concluded.