Introduction to Enzymes
Enzyme Kinetics: Basic Enzyme Reactions
Enzymes are catalysts and increase the speed of a chemical reaction without themselves undergoing any permanent chemical change. They are neither used up in the reaction nor do they appear as reaction products.
The basic enzymatic reaction can be represented as follows:
S + E → P + E 
where E represents the enzyme catalyzing the reaction, S the substrate, the substance being changed, and P the product of the reaction.