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Four pesticides P1 to P4 are reversible inhibitors of an enzyme E that is essential for the growth of a bacterium B. Their Ki values are given in the table below. Each of these four pesticides is used in four geographically different regions R1 to R4. The residual concentrations of these four pesticides in the respective regions are also shown in the table below:


Which pesticides will be able to inhibit bacteria ?

My question : I know that Ki shows the binding affinity. So, how is that related to residual concentration ? How can I deduce whether it will kill the bacteria or not ?

Unrelated question : Is it acceptable to use the word pesticide here ?!

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up vote 1 down vote accepted

Ki is the equilibration dissociation constant. The smaller this constant is, the stronger (more specific) is the binding between the inhibitor and the enzyme.

If the residual concentration is now higher than the Ki, for each molecule from the inhibitor which dissociates from the enzyme a new will bind (simply because of the concentration). If the concentration is lower (or much lower), this will not be sufficient to inhibit the enzyme. This assumes that the relation between enzyme, inhibitor and substrate are linear (and we are not getting some kind of saturation here).

Under the conditions mentioned above, P1 and P4 will inhibit the enzyme. For P2 and P3 the concentration is to low.

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