MEDizzy - A competitive reversible inhibitor such as physostigmine is

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Enzymes and Biochemistry of Digestion

A competitive reversible inhibitor such as physostigmine is used to treat glaucoma and myasthenia gravis and to reverse anticholinergic syndrome. Based on this, which one of the following statements is true concerning the clinical implications of using physostigmine?

ExplanationPhysostigmine is both a naturally occurring substance (Calabar bean) and a chemically synthesized substance that is a competitive reversible inhibitor of acetylcholinesterase. The drug easily crosses the blood-brain barrier. By definition, a competitive reversible inhibitor acts at the catalytic site with the substrate and competes with substrate binding to the enzyme. Thus, the effects of the inhibitor can be overcome by the addition of the substrate, leading to an effective reversal of drug overdose. This is a reversible inhibition, so the Vmax is unchanged because if sufficient substrate is added, the effects of the inhibitor can be overcome. With a competitive inhibitor, the Km is increased because more substrate is needed to reach 1=2 Vmax.