Question

i) When dihydrofolate reductase (10 Hg) was assayed in a total volume of 1 ml with 100 uM of dihydrofolate and 80 HM of deoxytubulosine, the enzyme activity was completely inhibited. After dialysis of the assay mixture, enzyme activity was fully restored. What does this tell you about the mode of inhibition by deoxytubulosine irreversible or reversible? For your answer, illustrate how this type of inhibition could occur. [2 marks] v) Suggest TWO types of binding interactions that may take place between deoxytubolosine and dihydrofolate reductase. Additionally for ONE of these interactions provide a structural modifications that would help you determine (after biological assays) if this interaction is significant or not. Use structures to assist your answer and explain your choices. [4 marks] deoxytubulosine

Answer 1

a) As it is already mentioned in the question that the dihydrofolate reductase will restored and regained its enzymatic activity , Thus the inhibition mode used by the inhibitor deoxytubulosine is Reversible Inhibition.

Reversible Inhibitor have always been able to give back the enzymatic activity due to the its weak interaction with the enzyme. These weak interactions are the result of non covalent interactions like hydrophobhic interactions etc. These inhibitors first attach to the enzyme and in this process, the latter loses all of its activity after that it removes itself from the enzyme and thus the nezyme will gain its enzymatic activity.

b) There are basically 2-3 types of bonding which can lead to the enzyme-inhibitor complex. The first one can be non covalent interactions in which there is no sharing of electrons like in covalent bonding take place rather , electromagnetic interactions takes place. Second could be the Irreversible Interactions in which the product formed would be more thermodynamically stable having less energy than the reactants.

The active site of the deoxytubulosine enzyme which can act as the active site must be the Nitogen containing residues as shown in the image below -

As the structure of the inhibitor is unknown, simple modifications can be seen through the above image.