Enzyme Kinetics: Measuring Inhibitory Effects and Determining Km and Vmax Values

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In summary, the conversation is about a practical involving the preparation of a calibration graph and using a spectrophotometer to measure absorbance. The results show a standard curve for glucose and fructose and an experiment with inhibitors fructose and urea. The questions ask for determination of initial reaction rates, Km and Vmax values, and mode of inhibition for fructose and urea. The conversation ends with the person asking for help to start the experiment and clarifying that they have the necessary data.
  • #1
Somebody please help me.


A calibration graph should be prepared by taking 0.0 (zero, blank), 1.0, 2.0 and 3.0 ml aliquots of an aqueous solution containing both 1.67 mM D-glucose and 1.67 mM D-fructose. Add distilled water to maket it 3 ml. Add 1 ml DNS reagent. Incubate 5 min. Add 3 ml distilled water.Measure with spectrophotometer 540 nm

Do the same with inhibitors


Standard curve

ml glucose/fructose Absorbance
0,----- 0.0
1,----- 0.69
2,----- 1.44
3,----- 2.15

ml sucrose No inhibitor + fructose +urea
0------------0.03------ 0.63------ 0.02
0.25-------- 1.08------ 0.97- ----- 0.43
0.5--------- 1.15------ 1.17- ----- 0.71
1.0--------- 2.29------ 1.71------- 1.02
1.5--------- 2.20------ 2.11------ 1.14

The standard curve drawn in terms of the molar concentration (in the 3 ml samples; not the volumes of standard mixture) of inverted sucrose (glucose + fructose) in the assay tubes.
From your results, determine:

1) the initial rates of reactions in units of mmole min-1 (ml diluted enzyme)-1
2) the Km and Vmax of the diluted enzyme, using the Lineweaver-Burk plot
3) determine the mode of inhibition for fructose and urea, and their Ki values using the Lineweaver-Burk plot

Please help me

I read around a lot but I just cannot start it

I wanted to use C1v1=C2V2 But I don't have the concentration

Please somebody at least tell me how to start it
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  • #2
Rather sketchily described.

A standard curve is an absorbance plotted against known concentrations of something. When you have a standard curve you can then use it to determine the unknown concentrations e.g. resulting from an enzyme reaction, by measuring absorbance. Your first table looks to be the calibration curve and looks reasonably linear.

Your second table might be the enzyme kinetic experiment, but you do not describe it. Was fructose the inhibitor? Does the third column represent measurement in the presence of an (unstated) constant concentration of fructose? What has urea to do with it?

Probably you have data that tells you the amount of (fructose + glucose) made in a certain time by hydrolysis of sucrose at varying concentrations. You say you don't, you would have to know the concentration of the sucrose solution you started with. You'd know that either from having weighed it out and made up the stock solution, or someone told you. You then know the concentration in the experiments since you pipetted various volumes to make a total volume you should also know.
  • #3
Thanks for your answer

Sorry panicked a little.

It is an enzyme kinetics practical with inhibitors fructose and urea.

I have the data that tells me the amount fructose/glucose and I put it in my question.

I have figured out a lot by myself but thanks for your answer.

Related to Enzyme Kinetics: Measuring Inhibitory Effects and Determining Km and Vmax Values

What is enzyme kinetics?

Enzyme kinetics is the study of the rates of chemical reactions catalyzed by enzymes. It involves measuring the speed at which substrates are converted to products by enzymes.

What factors affect enzyme kinetics?

The factors that affect enzyme kinetics include temperature, pH, enzyme and substrate concentrations, and the presence of inhibitors or activators.

How does temperature affect enzyme kinetics?

Temperature can affect enzyme kinetics by increasing the speed of the reaction up to a certain point (the optimal temperature), after which the enzyme can denature and lose its catalytic activity.

What is the Michaelis-Menten equation?

The Michaelis-Menten equation is a mathematical model that describes the relationship between substrate concentration and reaction rate in enzyme-catalyzed reactions. It is often used to determine the kinetic parameters of an enzyme, such as the maximum reaction rate (Vmax) and the substrate concentration at which the reaction rate is half of Vmax (Km).

How can enzyme kinetics be used in practical applications?

Enzyme kinetics has many practical applications, such as in the development of new drugs, understanding disease mechanisms, and optimizing industrial processes. It can also be used to study enzyme inhibition and activation, which has implications in the treatment of diseases and the production of certain products.

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