while calculating IC50 by using Graph pad prism, after conversion of conc. values to log X mode and normalising y axis, we need to select non-linear regression analysis. From this again we have to select dose-response inhibition, which shows again 4 options -
log (inhibitor)vs response (three parameters)
log (inhibitor)vs response--variable slope (four parameters)
log (inhibitor)vs normlised response
log (inhibitor)vs normalised response --variable slope
on what basis option has to be selected ?
if possible kindly explain in layman words.
If you have normalized your data, e.g. maximum inhibition is 100% (=1) and no effect is 0% (=0), then choose one of the last two options. If you use raw data, choose one of the first two options. The variable slope introduces an additional parameter (sometimes also referred to as Hill factor) that accounts for cooperativity. You should only choose the variable slope option, if you expect an allosteric or any other cooperative / anti-cooperative effect (often observed in multivalent systems). In case you have a single binding site, in which an inhibitor binds and competes a substrate, do not choose the variable slope.
If you do not have an standard drug as control in your experiment, in my opinion, it is not necessary to normalise the data.
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