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Introduction to Enzyme Kinetics

Introduction to Enzyme Kinetics

The purpose of this experiment is to measure the rates of reaction of the enzyme Alkaline Phosphatase with the substrate p-nitrophenol phosphate under varying conditions. The concentration of both substrate and enzyme were diluted and the inhibitor vanadate was utilized to determine whether or not the reaction is substrate or enzyme dependent and to see what type of inhibition vanadate was involved.

A class of proteins called enzymes catalyzes almost every chemical reaction in a cell. Enzymes increase the rates of reaction for those reactions, which are already energetically favorable, by lowering the activation energy. Enzymatic reactions differ from other chemical reactions, by having a higher reaction rates, greater specificity, and high capacity for regulation. Quite often, the rate of an enzymatically catalyzed reaction is 106-1010 times that of an uncatalyzed reaction under similar conditions. Enzymes are most effective under the optimal conditions of a cell, in which the cells aqueous environment is 37° C, and has a pH between 6.5-7.5.

Enzyme kinetics, the rate of reaction, and how this rate is influenced by different factors are directly correlated to the path followed by the reaction. For example, the enzyme-substrate reaction rate can be affected when there is a competitive inhibitor is involved. In the reaction, the competitive inhibitor competes with the substrate for the enzyme’s active site. This results in a lower reaction rate of the enzyme-substrate. On the other hand, noncompetitive inhibitors do not compete with the substrate for the active site and will not affect the affinity of the enzyme for its substrate, however, it will affect the maximum velocity of the reaction.

The catalytic action of an enzyme on a given substrate can be described by two parameters: Km (the Michaelis constant), which measures the affinity of an enzyme for its substrate, and Vmax, which measures the maximal velocity of the reaction at saturating substrate concentration. From the Michaelis-Menton complex:

E + S « ES « E + P

Where E is the enzyme, S is the substrate, and P is the product. The rate of product formation V can be dertermined by the equation below.

V= Vmax [S]/[S] + Km

From this equation, we can predict that when the V is independent from [S] the reaction would be zero order, whereas when V is dependent on [S], the reaction is first...

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