As long as there is substrate available to bind to, increasing enzyme concentration will speed up the enzymatic reaction. Once all of the substrate is bound, the reaction will no longer speed up with the increasing enzyme concentration, since there will be nothing for additional enzymes to bind to.

How Do Enzymes Work？

Enzyme is a catalytic protein which can speed up the chemical reaction without being altered in the reaction process. In the reaction process, there is no bond formed between the enzyme and the substrate, so the enzyme goes back to its original shape and can be used again. The enzyme binds to the substrate through the active site to form an enzyme-substrate complex. They are very specific in the reaction and also to the substrate they are binding with. When the shape of the substrate matches the active site of the enzyme, the function of the enzyme is correct, and their functioning is dependent on its three-dimensional structure. They make the reaction easier to occur by reducing the activation energy and activating more molecules, thus carrying out the catalyst.

Effect of Enzyme Concentration

The concentration of the enzyme is important in chemical reaction as it is needed to react with the substrate. Often a small amount of enzyme can consume a large amount of substrate. However, with the increase of enzyme concentration, the effectiveness of the active sites also increases, so these active sites will convert the substrate molecules into products. This basically means that if the concentration of the enzyme is to be increased, there needs to be an excess of substrate, in other words, which means that the reaction must be independent of the concentration of the substrate.

Zero-Order Reaction

In order to study the effect of increasing the enzyme concentration upon the reaction rate, the substrate must be present in an excess amount; i.e., the reaction must be independent of the substrate concentration. Any change in the amount of product formed over a specified period of time will be dependent upon the level of enzyme present. Graphically this can be represented as:

Figure 1. Zero-order reaction rate is dependent of substrate concentration.

These reactions are said to be "zero-order reactions" because the rates are independent of substrate concentration. The formation of product proceeds at a rate which is linear with time. The addition of more substrate does not serve to increase the rate. In zero-order kinetics, allowing the assay to run for double time results in double the amount of product.

The amount of enzyme present in a reaction is measured by the activity it catalyzes. The relationship between activity and concentration is affected by many factors such as temperature, pH, etc. An enzyme assay must be designed so that the observed activity is proportional to the amount of enzyme present in order that the enzyme concentration is the only limiting factor. It is satisfied only when the reaction is zero-order.

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