Describe the relationship between substrate concentration and the initial reaction rate of an enzyme-catalyzed reaction. Is this relationship linear? reaction goes. Start with the fact that the substrate concentration must be greater than the Km since we know that at the Km, the reaction proceeds at 1/2 Vmax. It has been shown experimentally that if the amount of the enzyme is kept constant and the substrate concentration is then gradually increased, the reaction .
Each enzyme is quite specific in character, acting on a particular substrates to produce a particular products.
Introduction to Enzymes
The central approach for studying the mechanism of an enzyme-catalyzed reaction is to determine the rate of the reaction and its changes in response with the changes in parameters such as substrate concentration, enzyme concentration, pH, temperature etc. This is known as enzyme kinetics. One of the important parameters affecting the rate of a reaction catalyzed by an enzyme is the substrate concentration, [S].
During enzyme substrate reaction, the initial velocity V0 gradually increases with increasing concentration of the substrate.
When we plot a graph with substrate concentration on the X axis and corresponding velocity on Y axis. It can be observed from the graph that as the concentration of the substrate increases, there is a corresponding increase in the V0.
At low enzyme concentrations or high substrate concentrations, all of the available enzyme active sites could be occupied with substrates.
Therefore, increasing the substrate concentration further will not change the rate of diffusion. In other words, there is some maximum reaction rate Vmax when all enzyme active sites are occupied.
The reaction rate will increase with increasing substrate concentration, but must asymptotically approach the saturation rate, Vmax. Vmax is directly proportional to the total enzyme concentration, E, and the cata lytic constant of the enzyme, kcat, which describes the frequency at which the enzyme-substrate complex is converted to product.
Substrate Concentration (Introduction to Enzymes)
How quickly enzyme active sites become saturated can be described by the variable K, the substrate concentration at which the reaction rate is Vmax. K is called the Michaelis-Menten constant after the scientists who originally derived it.
The reaction rate can be described by the equation where S is the substrate concentration. An enzyme with a low Km relative to the physiological concentration of substrate, as shown above, is normally saturated with substrate, and will act at a more or less constant rate, regardless of variations in the concentration of substrate within the physiological range.
An enzyme with a high Km relative to the physiological concentration of substrate, as shown above, is not normally saturated with substrate, and its activity will vary as the concentration of substrate varies, so that the rate of formation of product will depend on the availability of substrate.
If two enzymes, in different pathways, compete for the same substrate, then knowing the values of Km and Vmax for both enzymes permits prediction of the metabolic fate of the substrate and the relative amount that will flow through each pathway under various conditions.
In order to determine the amount of an enzyme present in a sample of tissue, it is obviously essential to ensure that the limiting factor is the activity of the enzyme itself, and not the amount of substrate available. This means that the concentration of substrate must be high enough to ensure that the enzyme is acting at Vmax.
In practice, it is usual to use a concentration of substrate about 10 - fold higher than the Km in order to determine the activity of an enzyme in a sample. If an enzyme is to be used to determine the concentration of substrate in a sample e.
The relationship is defined by the Michaelis-Menten equation: A number of ways of re-arranging the Michaelis-Menten equation have been devised to obtain linear relationships which permit more precise fitting to the experimental points, and estimation of the values of Km and Vmax.