Enzyme-substrate Complex

In a chemical reaction, the step wherein a substrate binds to the active site of an enzyme is called an enzyme-substrate complex. The activity of an enzyme is influenced by certain aspects such as temperature, pH, co-factors, activators, and inhibitors.
BiologyWise Staff
Enzymes are substances that play a crucial role in carrying out biochemical reactions. Chemically, they are proteinaceous in nature, which act on substrates to give the end result of the reactions called products. When a substrate binds to a specific enzyme, it is called an enzyme-substrate complex.
Thus, for any type of chemical reaction, there are three basic components, viz., substrate, enzyme, and product.
Let's discuss more regarding enzymes, enzyme-substrate complex, and the various aspects of enzymatic reactions in this BiologyWise article.
Enzyme Properties
All types of biological units require specific enzymes for specific reactions. The role of enzymes is to accelerate or catalyze the reaction, while remaining unchanged throughout the process. This action is achieved by reducing the activation energy required to initiate the chemical reaction. The rate of reaction varies significantly when performed with or without enzymes.
Each enzyme has a specific substrate, which is determined by its active site. As mentioned already, these compounds are proteins that have a globular structure. The amino acid arrangement in the active site is such that it is specific for recognizing only one type of a substrate. Thus, these complex proteins are very specific in terms of their substrates. This is also called enzyme-substrate specificity. For example, catalase enzyme decomposes hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2).
The Substrate Complex
While explaining the steps of a simple chemical reaction (involving only one substrate), the substrate molecule binds to the active site of the particular enzyme, forming an enzyme-substrate complex. For a better understanding, you can refer to the following simple representation of a chemical reaction:
E + S → ES → (EP) → E + P

In the above illustration, enzyme (E) binds with substrate (S), forming an enzyme-substrate complex (ES). Following the ES complex formation, E and S interaction takes place, resulting in an enzyme product (EP) complex. In the last step, the product (P) leaves the active site of the enzyme (E). The released product 'E' may be then recycled and combined with another substrate to form another product. This way, an enzyme acts on substrates to form products. The steps explained above are the three main steps of the cycle of enzyme-substrate interactions.
• The working mechanism of an enzyme in terms of its specificity is described by the lock-and-key model and induced-fit hypothesis. In the first model, the lock represents an enzyme and the key is the substrate. Like a key fits exactly into its specific lock, the enzyme and substrate fit accurately into each other.
• As per the induced-fit hypothesis, the enzyme undergoes certain structural changes after the substrate binds to the active site.
Overview of Enzyme-substrate Reactions
Some enzymes function independently without other substances, while many require other components. These additional, non-proteinaceous substances are referred to as cofactors. The compounds that carry molecules from one enzyme to other are called coenzymes. The enzyme-substrate activity is greatly influenced by certain substances, which can be grouped into two primary types: the enzyme activators and inhibitors.
As the name signifies, an activator enhances the rate of reaction, while the inhibitor slows down or inhibits the reaction. Studies clearly indicate that inhibitor molecules attach to the same active site, thus, blocking the binding of substrates. Enzyme inhibitors are medically employed as drugs and medicines for killing disease causing pathogens.
The formation of enzyme-substrate complex is also influenced by factors such as temperature and pH. In case of very high temperature, denaturation of the enzymes may take place. Likewise, pH of the medium affects the enzyme activity too. Hence, for controlling the rate of a particular chemical reaction, the temperature and pH should be regulated properly.