Enzyme Kinetics

Introduction

According to transition state theory, when molecules collide and a reaction occurs, they are temporarily stretched or less stable than the reactants or products. The potential energy of the activated complex increases during this transition stage, thereby forming an energy barrier between the reactants and products. Only when colliding reactants have enough energy to overcome this energy barrier would products be created. The activation energy (G) of a reaction represents the energy barrier. The lesser the number of effective collisions, the higher the activation energy for a particular reaction. Single-substrate and multiple-substrate mechanisms are the two types of enzyme mechanisms. The goal of kinetic studies on enzymes that only bind one substrate is to determine the enzyme’s affinity for that substrate as well as the turnover rate. When enzymes bind multiple substrates, enzyme kinetics can also reveal the order in which substrates bind and products are released.

The catalytic mechanism of Enzyme kinetics, its role in metabolism, how its activity is controlled, and how a drug or a modifier (inhibitor or activator) might influence the rate can all be revealed by studying its kinetics in this way. A protein molecule known as an enzyme (E) assists in the reaction of another molecule known as its substrate (S). This binds to the active site of the enzyme to produce an enzyme-substrate complex ES, which is subsequently transformed into an enzyme-product complex EP, and finally into product P through a transition state ES*. The sequence of steps is called a mechanism.

What are Enzyme Kinetics and Mechanisms

The enzyme-catalyzed reaction employs the same reactants as the uncatalyzed reaction and yields the same products. Enzymes, like other catalysts, do not change the substrate-product balance. Enzyme-catalyzed chemical processes, on the other hand, exhibit saturation kinetics, unlike uncatalyzed chemical reactions. The reaction rate increases linearly with substrate concentration for a given enzyme concentration and relatively low substrate concentrations; the enzyme molecules are largely free to catalyze the reaction, and increasing substrate concentration means more enzyme and substrate molecules encounter each other. The ability of an enzyme to be saturated with a substrate and the highest rate it can attain are two fundamental aspects of enzyme kinetics. Knowing these qualities can help you predict what an enzyme will perform in the cell and how it will react to changes in these settings. Because enzyme-catalyzed reactions are saturable, the rate of catalysis does not increase linearly as the substrate concentration rises. The reaction rate (v) rises as [S] grows when the beginning rate of the reaction is assessed over a range of substrate concentrations (denoted as [S]). The enzyme becomes saturated with the substrate as [S] increases, and the rate approaches Vmax, the enzyme’s maximal rate.

Michaelis-Menten Kinetics

Michaelis-Menten kinetics is an enzyme kinetics model that describes how the rate of an enzyme-catalyzed reaction is affected by the enzyme and substrate concentrations. Consider the following reaction: a substrate (S) binds reversibly to an enzyme (E) to create an enzyme-substrate complex (ES), which subsequently reacts irreversibly to generate a product (P) and release the enzyme.

S + E ⇌ ES → P + E

Within Michaelis-Menten kinetics, two key terms are:

Vmax-: When all of the enzyme’s active sites are saturated with substrate, it is the maximum rate of the reaction.

Km-: The substrate concentration at which the reaction rate is 50% of Vmax is known as Km (also known as the Michaelis constant). It is a measure of an enzyme’s affinity for its substrate; the lower the Km value, the more effective the enzyme is in performing its activity at lower substrate concentrations.

The reversible first step of the equation has a reaction rate constant of k+1 for producing the enzyme-substrate complex and k-1 for reversing the process. The reaction rate constant for the non-reversible second phase of the equation is k+2.

The following equation defines the rate of reaction (v), which is the rate at which the product is formed:

v = d[P]/DT = k+2[ES]

When we plot the rate of reaction versus the substrate concentration, we can see how the rate of reaction grows fast in a linear pattern as the substrate concentration increases (1st order kinetics). When the rate reaches a plateau, raising the substrate concentration does not influence the reaction velocity because all enzyme active sites are saturated with the substrate (0 order kinetics). The form of this plot of reaction rate vs. substrate concentration is a rectangular hyperbola. A Lineweaver–Burk plot, which shows the inverse of the reaction rate (1/r) against the inverse of the substrate concentration (1/[S]), is a more practical depiction of Michaelis–Menten kinetics.

The following is the equation that was used to create this plot:

1/V = {(Km/Vmax) *(1/S)} + (1/Vmax)

This creates a straight line, making it easier to grasp the graph’s numerous numbers and values. The graph’s y-intercept, for example, is the same as the Vmax. When assessing the kind of enzyme inhibition present, the Lineweaver-Burk plot may be used to compare the influence on Km and Vmax.

Conclusion

One of the most important procedures in evaluating an enzyme’s performance and industrial potential is to conduct enzyme kinetics research. In general, enzyme-catalyzed processes are out of equilibrium. The MM equation was used to calculate the maximum velocity of enzyme-catalyzed reactions as well as the substrate affinity for the enzyme. The Km should be utilized as a steady-state indication for a particular substrate concentration. When the substrate concentration is too low, the linear component of the reaction is evaluated. The earliest step of substrate transformation into product constants, for example, can help explain how enzymes operate and aid in the prediction of enzyme activity in live organisms. Both Vmax and Km are important in comprehending the human body’s metabolism. We can acquire a better knowledge of the enzymes and processes that occur in human metabolism by knowing the enzyme kinetic ppt constants. This knowledge might then be applied to enhance patient health outcomes in the medical field. The Km is a crucial parameter in biochemistry and enzymology because it determines the rate of substrate association, which is crucial in determining enzyme function.