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Section II – Enzymes: Kinetics, Mechanism, Regulation, & Role of Transition Metals

A protein engineer desires to alter the active site of chymotrypsin so that it will cleave peptide bonds to the C-terminal side of aspartyl and glutamyl residues. The protein engineer will be most likely to succeed if he replaces the hydrophobic amino acid at the bottom of the active site pocket with:

A. Phenylalanine

B. Threonine

C. Glutamine

D. Lysine

E. Proline

Select the one of the following statements that is NOT CORRECT.

A. Many mitochondrial proteins are covalently modified by the acetylation of the epsilon amino groups of lysine residues.

B. Protein acetylation is an example of a covalent modification that can be “reversed” under physiologic conditions.

C. Increased levels of acetyl-CoA tend to favor protein acetylation.

D. Acetylation increases the steric bulk of the amino acid side chains that are subject to this modification.

E. The side chain of an acetylated lysyl residue is a stronger base than that of an unmodified lysyl residue.

Select the one of the following statements that is NOT CORRECT.

A. Acid–base catalysis is a prominent feature of the catalytic mechanism of the HIV protease.

B. Fischer’s lock-and-key model explains the role of transition state stabilization in enzymic catalysis.

C. Hydrolysis of peptide bonds by serine proteases involves the transient formation of a modified enzyme.

D. Many enzymes employ metal ions as prosthetic groups or cofactors.

E. In general, enzymes bind transition state analogs more tightly than substrate analogs.

Select the one of the following statements that is NOT CORRECT.

A. To calculate Keq, the equilibrium constant for a reaction, divide the initial rate of the forward reaction (rate 1) by the initial velocity of the reverse reaction (rate 1).

B. The presence of an enzyme has no effect on Keq.

C. For a reaction conducted at constant temperature, the fraction of the potential reactant molecules possessing sufficient kinetic energy to exceed the activation energy of the reaction is a constant.


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