Question

1. Ketoconazole is an antifungal drug.
   1. Draw its structure and describe the protein that ketoconazole inhibits.
   2. Use excel to plot a curve for the enzyme activity of the target protein in Red (Km is 50nM and Vmax is 1.4 umol/min).
   3. Draw a curve in Blue where Ketoconazole alters the Km by 10-fold. What type of inhibitor is this?

Answer 1

a.

Ketoconazole inhibits C-14 α-demethylase (a cytochrome P450 enzyme), thus blocking the demethylation of lanosterol to ergosterol the principal sterol of fungal membranes.

b.

Km = 50 nM , Vmax = 1.4 umol/min

1/ Vmax = 0.714 = c (intercept)

Km / Vmax = 50/0.714 = 70.028 = m (slope)

y = mx + c

1/V0 = Km / Vmax(1/[s]) + 1/Vmax

1/V0 = 70.028(1/[s]) + 0.714

A lineweaver-burk plot (graph between 1/V0  vs 1/[s]) using this equation.

c.

if Km decreases by 10 fold

Km = 5 nM , Vmax = 1.4 umol/min

1/ Vmax = 0.714 = c (intercept)

Km / Vmax = 5/0.714 = 7.0028 = m (slope)

y = mx + c

1/V0 = Km / Vmax(1/[s]) + 1/Vmax

1/V0 = 7.0028(1/[s]) + 0.714

orange color depicts the enzyme activity with the inhibitor.

it is a type of competitive inhibitor, where Km decreases.