A 54- year-old man complains of an acute onset of unilateral eye pain and a reduction in the visual acuity. On physical examination, conjunctival injection (eye redness) and a mild-dilated and non-reactive pupil are observed. Fundoscopic examination reveals the cupping of the optic disc. Recognizing the signs and symptoms as glaucoma, the medication Acetazolamide is administered to decrease the production of aqueous fluid and lower the intraocular pressure. Acetazolamide is an inhibitor of carbonic anhydrase. The kinetic parameters are plotted in the graph. State the type of inhibition.
Case discussion
It is non-competitive enzyme inhibition. In non-competitive inhibition, binding of the inhibitor does not affect the binding of the substrate. The formation of both EI (enzyme inhibitor complex) and EIS (enzyme inhibitor substrate) complexes is therefore possible. However, while the enzyme-inhibitor complex can still bind substrate, its efficiency at transforming substrate to product, reflected by Vmax, is decreased. Noncompetitive inhibitors bind enzymes at sites distinct from the substrate-binding site and generally bear little or no structural resemblance to the substrate, Km value thus remains unaffected.
