Enzymes are proteins which enable chemical reactions in the body to occur many times more quickly than they otherwise would. In some cases, a reaction will not take place at all unless a specific enzyme is present. Along with pH, temperature and substrate concentration, enzyme concentration has an important effect on the reaction process. Assuming the amount of the substance, or substrate, taking part in the chemical reaction stays the same, a low concentration can lead to a chemical reaction occurring slowly. On the other hand, a high concentration can speed up a reaction, until a maximum possible rate is reached.
Each enzyme is specific to a particular chemical reaction or to a group of reactions. An attachment site on the enzyme binds its specific substrate while a reaction takes place. After the reaction, the substrate is released and the enzyme can be used again.
When studying enzyme concentration and observing its effect on a reaction, an experiment would normally begin with relatively low concentrations of the enzyme. This means that the substrate is usually present in excess at first. The rate of the reaction can be measured by the amount of product formed over time. As the enzyme solution becomes more concentrated, collisions between enzymes and substrate molecules are more likely to occur. This means that, as the concentration is increased, the rate of reaction speeds up in a linear fashion, until it reaches a certain level where it begins to flatten out.
The most efficient possible reaction occurs when every site on every enzyme is continually occupied by the substrate. Once this point has been reached, a higher enzyme concentration is required to increase the reaction rate. This makes new enzymes available to bind to the substrate. When all of the substrate molecules are attached to enzymes, increasing the enzyme concentration will no longer speed up the reaction process. The extra enzymes added will not have any spare substrate to work on, and the reaction rate remains level at the maximum limit.
If all of the factors which can alter reaction rates, such as pH, temperature and substrate concentration, are fixed, then measuring the rate of reaction becomes a way of measuring enzyme concentration. Reaction rate measurements are taken, and mathematical equations are used to define the amount of active enzyme accurately. When measuring concentrations, it is important to ensure that enough substrate is present to saturate all of the enzymes in the solution.