Enzymes Overview and Functions

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required for the reaction to occur.

The energy barrier that reactants must overcome to start a reaction.

The state where the forward and reverse reaction rates are equal, resulting in no net change in concentration of reactants and products.

The complex formed when an enzyme binds to its specific substrate.

The region on an enzyme where the substrate binds and the catalytic reaction occurs.

The enzyme's ability to bind to a specific substrate or a group of similar substrates.

The relationship between the amount of substrate and the rate of an enzymatic reaction. As substrate concentration increases, the reaction rate also increases until it reaches a maximum.

Factors that influence enzyme activity, including temperature, pH, substrate concentration, and the presence of inhibitors or activators.

Enzymes are biological catalysts that accelerate chemical reactions by lowering the activation energy required for the reaction to occur.

The activation energy is the minimum amount of energy required for a chemical reaction to occur. It represents the energy barrier that reactants must overcome to transform into products.

Enzymes achieve this by providing an alternative reaction pathway with a lower activation energy. This pathway is called the enzyme-catalyzed reaction, and it involves the formation of an enzyme-substrate complex.

The EC number is a four-digit numerical classification system that defines the specific catalytic activity of an enzyme. The first digit indicates the enzyme class, followed by three digits representing subclasses and sub-subclasses according to specific criteria.

The EC code numbers were developed to provide a systematic, standardized method to classify enzymes based on their catalytic activities. This system is used by scientists around the world to ensure clarity and consistency in enzyme nomenclature.

The standard abbreviations for enzymes are widely accepted and used in the United States and internationally, facilitating communication and consistency in scientific reports and research.

In enzymatic reactions, ATP is frequently used as an energy source. The breaking of the pyrophosphate bond in ATP releases energy, which is often coupled with the joining of two substrate molecules by the enzyme.

The combination of an enzyme and its substrate is called an enzyme-substrate complex. This interaction facilitates the chemical reaction by bringing the reacting molecules into close proximity and in the correct orientation for the reaction to occur.

The rate of an enzyme-catalyzed reaction increases as the substrate concentration increases until it reaches a maximum velocity (Vmax) where the enzyme is saturated with substrate.

The Michaelis-Menten constant (Km) is a measure of the substrate concentration at which the reaction velocity is half of its maximum value (Vmax).

When the enzyme is saturated with substrate, the reaction velocity reaches its maximum value (Vmax). Further increasing the substrate concentration will not increase the reaction rate.

The Michaelis-Menten equation describes the relationship between the reaction velocity (V), maximum velocity (Vmax), substrate concentration ([S]), and the Michaelis-Menten constant (Km).

First-order kinetics describes a reaction where the reaction rate is directly proportional to the substrate concentration. This occurs when there is an excess of enzyme over substrate.

Zero-order kinetics describes a reaction where the reaction rate is independent of the substrate concentration. This occurs when the enzyme is fully saturated with substrate.

The rate-limiting step in an enzymatic reaction is the formation of product and enzyme from the enzyme-substrate complex (ES).

The Michaelis-Menten model assumes that the binding of substrate to enzyme is reversible and that the equilibrium between the enzyme, substrate, enzyme-substrate complex, and product is established rapidly. The model also assumes that the reaction of product with free enzyme to form the enzyme-substrate complex is negligible.

The maximum velocity of a reaction catalyzed by an enzyme. It represents the point where all enzyme active sites are saturated with substrate.

A measure of the affinity of an enzyme for its substrate. It represents the substrate concentration at which the reaction rate is half of Vmax.

A graphical representation of the Michaelis-Menten equation. This plot involves plotting the reciprocal of the initial reaction velocity (1/v) against the reciprocal of the substrate concentration (1/[S]).

The process of altering an enzyme's structure and function due to changes in environmental conditions like temperature or pH.

The pH at which an enzyme exhibits maximum activity. This represents the optimal pH for an enzyme.

The temperature at which an enzyme displays its peak activity, signifying the most favorable temperature for function.

The increase in reaction rate directly proportional to the increase in enzyme concentration, as long as substrate concentration exceeds enzyme concentration.

The effect of increasing temperature on enzyme activity. Initially, reaction rate increases with temperature, but eventually, denaturation occurs due to excessive heat.

A type of enzyme inhibition where the inhibitor binds to the enzyme at a site different from the active site, affecting the enzyme's ability to bind substrate or catalyze the reaction.

A type of enzyme inhibition where the inhibitor binds only to the enzyme-substrate complex, preventing the complex from forming product.

An enzyme inhibition mechanism where the inhibitor can bind to either the enzyme or the enzyme-substrate complex, affecting both the enzyme's affinity for the substrate and its ability to catalyze the reaction.

A method of measuring enzyme activity by determining the amount of substrate consumed, product produced, or coenzyme consumed/produced in a given time.

A reaction condition where the amount of substrate is so high that the enzyme is essentially saturated, and the reaction rate is determined solely by the enzyme's ability to catalyze the reaction.

A coenzyme that is often measured in the laboratory. It absorbs light at 340 nm, making it convenient to monitor its change in concentration.

A continuous assay involves measuring the absorbance at specific time intervals, providing a detailed view of the reaction's progress. This approach is ideal for verifying the reaction's linearity and identifying any deviations.

Enzyme activity is often reported in units of activity, reflecting the enzyme's ability to catalyze a specific reaction. The international unit (IU) defines the amount of enzyme that transforms 1 micromole of substrate per minute under defined conditions.

Deviation from linearity in an enzyme assay typically arises when the enzyme concentration outpaces the available substrate. The reaction slows down as the substrate is depleted, indicating a shift from zero-order kinetics.

Continuous monitoring of an enzyme assay allows detection of sudden drops in reaction rate, indicating a potential deviation from linearity. This allows for immediate adjustments such as sample dilution, ensuring accurate results.

To standardize enzyme activity measurements, the EC uses the international unit (IU), which represents the amount of enzyme catalyzing the conversion of 1 micromole of substrate per minute under specific conditions.

If an enzyme assay shows a decrease in reaction rate due to high enzyme concentration, reducing the sample amount through dilution can restore linearity and improve the accuracy of the results.

A katal, the SI unit for enzyme activity, is defined as the amount of enzyme that transforms 1 mole of substrate per second under specified conditions.