Question

Prostaglandins are a class of eicosanoids, fatty acid derivatives with a variety of extremely potent actions on vertebrate tissues. They are responsible for producing fever and inflammation and its associated pain. Prostaglandins are derived from the 20-carbon fatty acid arachidonic acid in a reaction catalyzed by the enzyme prostaglandin endoperoxide synthase. This enzyme, a cyclooxygenase, uses oxygen to convert arachidonic acid to PGG₂, the immediate precursor of many different prostaglandins.

Arachidonic acid (mM)	Rate of formation of PGG2 (mM/min)	Rate of formation of PGG2 with 10 mg/ml ibuprofen (mM/min)
0.345	16.7	10.4
0.414	18.8	12.0
0.621	23.7	16.1
1.04	30.0	22.1
2.42	38.9	32.4

The kinetic data given in the table are for the reaction catalyzed by a mutant of prostaglandin endoperoxide synthase. Focusing here on the first two columns, determine the VmaxVmax and KmKm of the enzyme.

Vmax=Vmax=

mM/minmM/min

Km=Km=

mMmM

Ibuprofen is an inhibitor of prostaglandin endoperoxide synthase. By inhibiting the synthesis of prostaglandins, ibuprofen reduces inflammation and pain.

Using the data in the first and third columns of the table, determine the type of inhibition that ibuprofen exerts on prostaglandin endoperoxide synthase.

uncompetitive inhibition

mixed inhibition

competitive inhibition

Answer 1

With the increase in the concentration of arachidonic acid the rate of prostaglandin synthesis also increases since the concentration of enzyme is directly proportional to the concentration of substrate rate of velocity also increases and reaches to a steady state value as all the active sites of the enzyme are occupied by substrate

With the presence of ibuprofen the rate of synthesis decreases slowly which means the drug binding with the enzyme with very weak covalent forces and can be easily displaced by the substrate is an non-competitive inhibitor