# Online calculation of km and vmax relationship

### Calculation ofKm and Vmax from Substrate Concentration Pages 1 - 3 - Text Version | FlipHTML5

Very Simple KM Vmax Tool Kit. Determine KM and Vmax by online curve-fitting & get quality plots! Point style: x +. Colour option: Colour Black and white (higher. I'm trying to calculate the kcat for the enzyme sample that I have from the following . Catalytic efficiency is actually the ratio kcat/Km. In your case Vm is expressed as Could you please elaborate the equation you used to solve the problem? . I need help with figuring out what units to use for my calculation for Kcat. Biochemists calculate Km for an enzyme reaction by creating a At the point at which KM = [S], this equation reduces to V = Vmax ÷ 2, so KM is.

By measuring the rate of sub-strate utilization v at different substrate con- Substitution of another K,, value K2 will yieldcentrations sKm and Vmax can be calculated another value for b and a slope max Fig. The disadvantage The deviation of b from zero can be used toof this approach is that during the measurement,substrate concentrations change continuously calculate the real Km and Vmax values Fig.

The exact value for Km can be calculated when Km, and Km are plotted against Vmax andAlso, many measurements at different substrate Vmax.

## Michaelis-Menten Equation Calculator

At the real Vmax value, the correspondingconcentrations are needed. In this note we pre- real Km is found Fig. With this method, Kmsent a more direct method of determining K,, and Vmax values can thus be obtained directlyand Vmax based on equation 1.

When during a from concentration plotted versus time in a re-reaction substrate concentrations are measuredas a function of time t Fig. Calculations were carried out with a pro-determine Km and Vm.

With this method it is easy to Integration of equation 1 yields: Many such computer programs are currently available and, if not, the programming skill involved is usually fairly low. If the mechanism is not known, initial attempts are usually made to fit the data to the Michaelis-Menten kinetic model. Its use also ensures that there is no effect of reaction reversibility or product inhibition which may affect the integral method based on equation 1.

### Determination of Vmax and Km

Alternatively the direct linear plot may be used Figure 1. This is a powerful non-parametric statistical method which depends upon the assumption that any errors in the experimentally derived data are as likely to be positive i.

It is common practice to show the data obtained by the above statistical methods on one of three linearised plots, derived from equation 1. Of these, the double reciprocal plot is preferred to test for the qualitative correctness of a proposed mechanism, and the Eadie-Hofstee plot is preferred for discovering deviations from linearity.

The direct linear plot. A plot of the initial rate of reaction against the initial substrate concentration also showing the way estimates can be directly made of the Km and Vmax. Every pair of data points may be utilised to give a separate estimate of these parameters i. This is because it takes a large amount i. Thus, Km is a very useful parameter by which the affinity of the protein for various substrates can be compared.

It is important to emphasize that the kinetics of transport for many transport proteins exhibit features that are very similar to those of enzymes. Similar to enzymes, transporters show specificity with respect to the substrate transported and, in addition, the rate of substrate transport across a biological membrane exhibits saturation at high substrate concentrations. Therefore, the kinetics of many transport processes can be studied by using Michaelis-Menten kinetics.

The Michaelis-Menten equation can adequately describe the dependence of transport rate on the substrate concentration for facilitative transporters, secondary active transporters cotransporters and exchangersand primary active transporters i. If the protein under study has more than one i. In this case, the Michaelis-Menten equation is no longer the appropriate equation to use for studying the rate of reaction as a function of the substrate concentration.

Instead, the Hill equation is the appropriate equation to use. Indeed, the Michaelis-Menten equation is a special case of the Hill equation where the protein under study has only one substrate binding site. Vmax is the maximum velocity of the reaction. It has the same units as the reaction velocity V.

It is the highest reaction rate that can be achieved at saturating substrate concentrations. Km is the Michaelis constant. Km has the same units as the substrate concentration. Km provides useful information about the "apparent affinity" of the protein under study enzyme, transporter, etc. Affinity can be thought of as how tightly the substrate binds to the enzyme or transporter protein.

The lower the numerical value of Km, the higher the apparent affinity for the substrate i.