Enzymes: Biological Catalysts and Their Functions

What Is an Enzyme?

An enzyme is a protein that acts as a biological catalyst. Its primary function is to increase the rate of a natural chemical reaction. Enzymes typically react with one specific substrate, and their activity is regulated within the cell through various means, including inhibitors and activators.

Enzyme Structure

Most enzymes are proteins with three-dimensional shapes determined by their specific amino acid sequences.

Key Concepts in Enzyme Activity

• Substrate: When a substrate molecule binds to the highly specific active site of an enzyme, an enzyme-substrate complex is formed. This complex modifies the substrate and initiates a series of chemical reactions, resulting in the formation of a product.
• Transition State: The highest energy structure along the reaction coordinate between reactants and products for every step of a reaction mechanism.
• Activation Energy: The minimum energy required to start a chemical reaction.
• Active Site: The region of an enzyme where substrate molecules bind and undergo a chemical reaction. It consists of residues that form temporary bonds with the substrate (binding site) and residues that catalyze the reaction.
• Products: The molecules remaining after an enzyme binds with and acts upon a substrate.

Factors Affecting Enzyme Activity

Temperature and pH: Temperature affects the rate at which substrate and enzyme molecules bind. Suboptimal temperatures result in less contact between enzymes and substrates, which slows the frequency and rate of reaction.

Optimal Conditions

While reactions slow down when conditions are not optimal, extreme temperatures can be detrimental. Under very high temperatures, the weak hydrogen bonds of the enzyme tend to break, causing the rate of reaction to decrease or stop entirely.

Amylase: A Practical Example

Amylase is an enzyme that catalyzes the hydrolysis of starch into sugars. It is commercially important in the production of syrups, food products, fermentation, and brewing processes (glucose-amylase, short oligosaccharides, maltotriose, maltose). Amylase is also present in the saliva of humans and some other mammals, where it initiates the chemical process of digestion.