Good afternoon, I am an undergraduate student currently doing my research on inhibitory effect of plant extracts on digestive enzymes. How to calculate IC50 for inhibitory effects of plant extracts on digestive enzymes?
IC50 can be determined by interpolation or extrapolation of a dose-response curve using GraphPad Prism software.
Or You can take different concentration of plant extract and calculate percentage inhibition of respective extract for different concentration. Now plot a graphs concentration v/s percentage inhibition. where concentration at X axis and percentage inhibition at Y axis. now interpolate 50% inhibition from Y axis to dose response curve or line of origin and again interpolate down to X axis in order to discover concentration that is IC 50. IC50 means the concentration of extract at which 50% inhibition exhibited. Remember, your percentage inhibition of lower dose should be less that 50% and higher dose should more that 50%. accordingly select different concentration of extract. 1, 2, 4, 8, 10 microgram, or 0.1, 0.2, 0.4, 0.8 microgram and 1, of, 10, 20, 40, 80, 100 microgram in your reaction mixture.
There is a misunderstanding, IC50 cannot be calculated for an enzyme. Which is the "digestive" enyzme you are investigating?
Yes, one of the best sofware is GraphPad where you can perform non linear regression plotting plant extract concentration in the X axis versus inhibitory percentage of the enzyme in the Y axis. You will just have to choose the best fit. GraphPad is always better than Excel for this type of calculations.
Dear Prof. Rafael Franco,
Can you kindly elaborate the fact regarding IC50 of enzyme. We have seen several articles, where IC50 calculated for enzymes. I am interested to know about digestive enzyme.
Parameters for enzymes are Km (Michaelis constant)t and Ki, contant of inhibition. You need first to know which type of inhibitor is yours. If unknown you have to test for either copetitive, noncompetitite and uncompetitive. Anf finalyy you calculte Ki. It is relatively easy and you have to meausre the activity versus different concentrations of substrate and the same in the presence of at least 3 concentrations of inhibitor. From all data you may both calculate the type of inhibitor and the Ki. If IC50 is in any paper it is fully misleading for an enzyme and its inhibitor. If you tell me in which paper I may figure out what is behind such "IC50"
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