Cyclooxigenases (COXs) are enzymes found in cells that produce prostaglandins Ex
ID: 51946 • Letter: C
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Cyclooxigenases (COXs) are enzymes found in cells that produce prostaglandins Excess prostaglandins can result in inflammation and pain. Thus, many pain relievers such as aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs). are inhibitors of this enzyme. Inhibitors can reduce the velocity of enzymatic reactions. Different inhibitors do this in different ways, which can alter how effective they are Consider the graph below. Given this data and the information above, 5. What is the Vmax normally of COX alone? How does the addition of aspirin affect the Vmax of the reaction catalyzed by COX? 6. When [S] = 10, what is the approximate velocity of the reaction (prostaglandin production) in the presence of aspirin? 7. In an effort to make a better over-the-counter pain reliever, a company is testing NSAID2. They have acquired 4 data points, each marked by an X on the graph, to determine how this drug changes COX function. Using this data, write an equation that describes the effect of NSAID2 on prostaglandin production. Use this model to predict the Vmax of the COX-catalyzed reaction in the presence of NSAID2. 8. Some inhibitors are reversible, which means addition of more substrate can overcome the inhibition. Given the fact that the x-intercept = -1/Km, determine which inhibitor (Aspirin or NSAID2) is reversible, and which is irreversible (for any amount of substrate, the reaction is still inhibited)Explanation / Answer
5. Lineweaver-Burk plot
The slope of the line gives Km/ Vmax and the Y intercept give - 1/Km
Here Y intercept is -0.3. Hence -0.3 = - 1/Km Hence, 0.3 Km = 1, Km = 1/0.3; Km = 3.33
Slope of the line can be found by the equation X2 - X1 / Y2 - Y1 = Km/Vmax; lets take 0.5 and 0.9 of X and 0.3 and 0.4 of y hence by substituting here, 0.1/0.4 = Km/Vmax; 0.25 = 3.33/ Vmax; Vmax = 3.33/0.25 = 13.32.
Hence Vmax for COX alone is 13.32.
6. When (S) = 10 , The velocity of the reaction of prostaglandin in presence of aspirin is 0.38 based on the graph.
7. Here lets take X1 and X2 as 0.4 and 0.5 and Y1 and Y2 as 0.5 and 0.6; By substituting we get Km/Vmax = 1. In this equation Km = Vmax; The Km of the reaction in the presence of inhibitor is same as the reaction in the presence of aspirin and cox alone which is 13.32.
8. When the point of Y intercept is similar for all the compounds it is said to inhibit competitively, here the inhibitor has no effect on the Vmax of the enzyme. Here the the graph represents a non- competitive inhibition hence increase in the inhibitor concentration changes both Vmax and Km of the enzyme. Hence it is a reversible inhibitor when we increase the substrate concentration the enzyme can revert back to its normal state.
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