MCAT Question of the Day
    •

    Q:

    		 Sildenafil (viagra) is a common treatment for male erectile dysfunction. It acts through inhibition of PDE5 (phosphodiesterase type 5) in order to prevent the degradation of a cGMP (the substrate for PDE5). This, in turn, allows for smooth muscle relaxation and erection in the penis. The inhibition dynamics of sildenafil are examined through measuring the catalytic rate of PDE5 in the presence of the drug. It is found that doubling cGMP concentration has almost no effect on the catalytic rate. Which of the following is possible for sildenafil?
    		 

    A

    		 PDE5 inhibition by sildenafil can be saturated and diminished with enough addition of cGMP

    B

    		 Decreasing cGMP concentrations will decrease the catalytic rate of the reaction

    C

    		 Decreased cGMP levels will result in an increase in catalytic rate

    D

    		 Sildenafil is a noncompetitive inhibitor



    Control of Enzyme Activity |
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