Diisopropylfluorophosphate (DIFP) inactivates chymotrypsin bycovalently modifyin
ID: 5371 • Letter: D
Question
Diisopropylfluorophosphate (DIFP) inactivates chymotrypsin bycovalently modifying Serine-195. This occurs becausea. DIFP looks like the substrate for chymotrypsin andbinds in the active site as a competitive inhibitor
b. Serine-195 is in an environment which gives it a higherthan normal reactivity with respect to DIFP
c. DIFP randomly modifies all serine residues on theprotein and if enough is added the one in the active site willeventually be modified
You have isolateda new protease that cleaves peptide bonds following Asp and Glu.Based on its inactivation by DIFP, you suspect that it may utilizea mechanism similar to chymotrypsin. The difference in specificitymight be explained by
a. The presence of a positively charged residue in the S1binding pocket
b. The presence of a negatively charged residue in the S1binding pocket
c. Replacement of Serine-195 with a positively chargedresidue
Basedon the active sites of cysteine proteases, aspartyl proteases, andmetalloproteases, which would you expect might have a covalentintermediate involved in its mechanism?
a. Cysteine proteases
b. Aspartyl proteases
c. Metalloproteases
What commonmechanistic feature do metalloproteases, carbonic anhydrase, andthe EcoRV restriction enzyme have in common?
a. All three active sites contain Zn(II)
b. All three use metal ions to activate watermolecules
c. All three perform hydrolytic reactions
The alteration of enzyme structure on binding of a substrate toan active site is referred to as
a. Enzyme denaturation
b. Enzyme inhibition
c. Induced fit
Explanation / Answer
Diisopropylfluorophosphate (DIFP) inactivates chymotrypsin by covalently modifying Serine-195. This occurs because serine-195 is in an environment that gives it a higher than normal reactivity with respect to DIPF.
Hence, the correct option is B.
The correct option is a. the presence of a positively charged residue in the S1 binding pocket.