Enzyme-substrate Complex

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.

Enzyme Properties
All types of biological units require specific enzymes for specific reactions. The role of enzymes is to speedup or catalyze the reaction, while remaining unchanged throughout the process. This action of enzymes is achieved by reducing the activation energy required to initiate the chemical reaction. The rate of reaction varies significantly, when performed with enzymes and without enzymes.

Each enzyme has a specific substrate, which is determined by its active site. As mentioned already, enzymes 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, enzymes 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 better understanding, you can refer to the following simple representation of a chemical reaction:

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, enzyme substrate 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 enzyme may be then recycled and combined with another substrate to form a product. This way an enzyme acts on substrates to form products.

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 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. And compounds that carry molecules from one enzyme to others are called coenzymes. The enzyme substrate activity or more precisely, the enzyme activity is greatly influenced by certain substances, which can be grouped into two primary types, the enzyme activators and enzyme inhibitors.

As the name signifies, an enzyme activator enhances the rate of reaction, while the enzyme inhibitor slows down or inhibits the reaction. Studies have shown 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. Read more on enzymes in the body.

The formation of enzyme-substrate complex is also influenced by temperature and pH. In case of very high temperature, denature of the enzymes may take place. Likewise, pH of the medium affects the enzyme activity. Hence, for controlling the rate of a particular chemical reaction, the temperature and pH should be regulated properly.