30 microM ibuprofen Ignore potential difficulties of using this type of plot a)
ID: 879150 • Letter: 3
Question
30 microM ibuprofen
Ignore potential difficulties of using this type of plot
a) estimate the apparent values of Vmax and Km for the reactions in the presence and absence of ibuprofen
b)from the date shown above,, does ibuprofen interact with the free enzyme, the enzyme substrate complex or both? carefully explain your reasoning
c) would you expect ibuprofen to be more effective as an inhibitor under conditions of high or low substrate concentrations? again carefully explain you reasoning
d) assuming that the reactions contained 1*10^-8 M enzyme what is Kcan for the enzyme? does the inhibitor change K cat?
e) From the date given abvoe, calculate the inhibition constant Ki for inbuprofen.
2. in contast to inbprofen, aspirin is an irreversible inhibitor of PGH2 synthase, reacting with a Ser residue in the active site. you have incubated 5 microM enzyme with 1 mM aspirin and have found that 85 % of the enzyme was inactivated in 30 min.
a) calculate the psedo-first-order rate constant for the reaction under these condistions
b) calculate the second order rate constant for the inactivation of PHG2 by asprin
c) suppose that you wanted to use 5mM aspirin and inactivate 99% of the enzyme. for how long should you allow the reaction to proceed?
d) suppose that you incubate 1 microM enzyme with 1mM aspirin for 30 min. would you expect more or less than 85 % of the enzyme to be inactivated? explain your reasoning
e) suppose that you incubate 1 mM enzyme with 1mM aspirin for 30 min. would you expect more or less than 85 % of the enxyme to be inactivated? explain your reasoning.
+lbuprofen 0.2 -Ibuprofen 2 0.1 -0.2 0.2 0.4 0.6 1/IS] (uM-1) immore the potential difficultieExplanation / Answer
a) from the above graph 1/Vmax = intercept = 0.075
Vmax = 1/0.075 = 13.33
Km/[S]Vmax = 1/Vo -1/Vmax = 0.1-0.075 = 0.025
Km = 0.025(0.1)(13.33) = 0.033
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