Problem 1
What are the four basic catalytic strategies used by many enzymes?
Problem 2
Many isolated enzymes, if incubated at \(37^{\circ} \mathrm{C},\) will be denatured. However, if the enzymes are incubated at \(37^{\circ} \mathrm{C}\) in the presence of substrate, the enzymes are catalytically active. Explain this apparent paradox.
Problem 3
Succinylcholine is a fast-acting, short-duration muscle relaxant that is used when a tube is inserted into a patient's trachea or when a bronchoscope is used to examine the trachea and bronchi for signs of cancer. Within seconds of the administration of succinylcholine, the patient experiences muscle paralysis and is placed on a respirator while the examination proceeds. Succinylcholine is a competitive inhibitor of acetylcholinesterase, a nervous system enzyme, and this inhibition causes paralysis. However, succinylcholine is hydrolyzed by blood-serum cholinesterase, which shows broader substrate specificity than does the nervous system enzyme. Paralysis lasts until the succinylcholine is hydrolyzed by the serum cholinesterase, usually several minutes later. (a) As a safety measure, serum cholinesterase is measured before the examination takes place. Explain why this measurement is good idea. (b) What would happen to the patient if the serum cholinesterase activity were only 10 units of activity per liter rather than the normal activity of about 80 units? (c) Some patients have a mutant form of the serum cholinesterase that displays a \(K_{M}\) of \(10 \mathrm{mM},\) rather than the normal 1.4 mM. What will be the effect of this mutation on the patient?
Problem 5
Match the term with the description or compound. (a) Competitive inhibition_____ (b) Uncompetitive inhibition_____ (c) Noncompetitive inhibition_____ 1\. Inhibitor and substrate can bind simultaneously 2\. \(V_{\text {max }}\) remains the same but the \(K_{\mathrm{M}}^{\text {app }}\) increases 3\. Sulfanilamide 4\. Binds to the enzymesubstrate complex only 5\. Lowers \(V_{\max }\) and \(K_{M}^{\text {app }}\) 6\. Roundup 7\. \(K_{M}\) remains unchanged but \(V_{\text {max }}\) is lower 8\. Doxycycline 9\. Inhibitor binds at the active site
Problem 8
What are the four key types of irreversible inhibitors that can be used to study enzyme function?
Problem 9
Some bacteria produce the enzyme \(\beta\) -lactamase, which cleaves and opens lactam rings. How would the presence of \(\beta\) -lactamase affect bacterial sensitivity to penicillin?
Problem 10
What is the catalytic triad, and what are the roles of the individual components in chymotrypsin activity?
Problem 11
What is the purpose of the oxyanion hole in chymotrypsin?
Problem 13
If chymotrypsin is such an effective protease, why doesn't it digest itself?
Problem 14
Picture in your mind the velocityversus-substrate concentration curve for a typical MichaelisMenten enzyme. Now, imagine that the experimental conditions are altered as described below. For each of the conditions described, fill in the table indicating precisely (when possible) the effect on \(V_{\max }\) and \(K_{M}\) on the imagined Michaelis-Menten enzyme. Experimental condition \(V_{\max } \quad K_{M}\) (a) Twice as much enzyme is used. (b) Half as much enzyme is used. (c) A competitive inhibitor is present. (d) An uncompetitive inhibitor is present. (e) A pure noncompetitive inhibitor is present.
