CH 8

Flashcards based on the lecture notes from Chapter 8, covering enzyme mechanisms, kinetics, and inhibition.

What is covalent catalysis?

The active site contains a nucleophile that is briefly covalently modified.

What is general acid-base catalysis?

A molecule other than water donates or accepts a proton.

What role do metal ions play in metal ion catalysis?

Serve as an electrophilic catalyst.

What is catalysis by approximation and orientation?

The enzyme brings two substrates together in an orientation that facilitates catalysis.

What environmental factors affect enzyme activity?

Temperature, pH, and inhibitory molecules.

What effect does pH have on enzyme activity?

Most enzymes have an optimal pH.

What is competitive inhibition?

The inhibitor is structurally similar to the substrate and can bind to the active site, preventing the actual substrate from binding.

What is uncompetitive inhibition?

The inhibitor binds only to the enzyme-substrate complex.

What is noncompetitive inhibition?

The inhibitor binds either the enzyme or enzyme-substrate complex.

How does competitive inhibition affect Vmax and KM?

Vmax of the enzyme is unchanged, but the apparent value of KM is increased.

How does uncompetitive inhibition affect Vmax and KM?

Vmax is lower, and KM is lower.

How does noncompetitive inhibition affect Vmax and KM?

Vmax is lower, and KM is not changed.

What is the key characteristic of irreversible inhibitors?

Bind very tightly to enzymes.

What do group-specific reagents do?

React with R groups of specific amino acids.

What are affinity labels (substrate analogs)?

Are structurally similar to the enzyme’s substrate but inhibit the enzyme by covalently modifying an amino acid in the active site.

What are suicide inhibitors (mechanism-based inhibitors)?

Bind to the enzyme as a substrate, leading to irreversible inactivation.

What peptide bonds does chymotrypsin hydrolyze?

Hydrolyzes peptide bonds selectively on the carboxyl side of large hydrophobic amino acids.

What is the role of serine 195 in chymotrypsin catalysis?

Serine 195 becomes a nucleophile that attacks the carbonyl group of the protein substrate.

What is the purpose of chromogenic substrates?

Generate colored products, facilitating enzymatic studies.

What are the two steps in chymotrypsin catalysis?

Acylation: rapid formation of an acyl-enzyme intermediate. Deacylation: slower release of the acyl group, regenerating the free enzyme.

What does TPCK do?

Covalently modifies histidine 57 in chymotrypsin, leading to a loss of enzyme activity.

What are the roles of histidine 57 and aspartic acid 102 in the catalytic triad?

Histidine 57 removes a proton from serine 195, generating a highly reactive alkoxide ion. Asp 102 orients the histidine and renders it a better proton acceptor.

What is the function of the oxyanion hole?

Stabilizes the tetrahedral reaction intermediate.

What is the function of the S1 pocket?

Binds to a residue on the substrate and positions the adjacent peptide bond for cleavage.

Give one example of an irreversible inhibitor?

Penicillin, phenylmethanesulfonyl fluoride (PMSF) and Allopurinol.