When Km value for an enzyme is low, its affinity is considered to be high for its substrate. Considering this concept, does it mean that high affinity always leads to. Since KM has the same units as substrate concentration, this implies a relationship between KM and KM is constant for any given enzyme/substrate pair Km is a measure of ES binding; relative measure of the affinity of a. A high Km means a lot of substrate must be present to saturate the enzyme, meaning the enzyme has low affinity for the substrate. On the other hand, a low K m.
Kcat is equal to K2, and it measures the number of substrate molecules "turned over" by enzyme per second. The reciprocal of Kcat is then the time required by an enzyme to "turn over" a substrate molecule.
The higher the Kcat is, the more substrates get turned over in one second. Km is the concentration of substrates when the reaction reaches half of Vmax. A small Km indicates high affinity since it means the reaction can reach half of Vmax in a small number of substrate concentration. This small Km will approach Vmax more quickly than high Km value. The enzyme efficiency can be increased as Kcat has high turnover and a small number of Km.
Taking the reciprocal of both side of the Michaelis-Menten equation gives: To determined the values of KM and Vmax. The double-reciprocal of Michaels-Menten equation could be used. Lineweaver-Burk graphs are particularly useful for analyzing how enzyme kinematics change in the presence of inhibitors, competitive, non-competitive, or a mixture of the two.
There are three reversible inhibitors: They can be plotted on double reciprocal plot. Competitive inhibitors are molecules that look like substrates and they bind to active site and slow down the reactions.
Structural Biochemistry/Enzyme/Michaelis and Menten Equation
Therefore, competitive inhibitors increase Km value decrease affinity, less chance the substrates can go to active siteand Vmax stays the same. The rate of formation of product now depends on the activity of the enzyme itself, and adding more substrate will not affect the rate of the reaction to any significant effect.
The rate of reaction when the enzyme is saturated with substrate is the maximum rate of reaction, Vmax. The relationship between rate of reaction and concentration of substrate depends on the affinity of the enzyme for its substrate.
This is usually expressed as the Km Michaelis constant of the enzyme, an inverse measure of affinity.
For practical purposes, Km is the concentration of substrate which permits the enzyme to achieve half Vmax. An enzyme with a high Km has a low affinity for its substrate, and requires a greater concentration of substrate to achieve Vmax. 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: