David L Nelson and Michael M Cox LEHNINGER

David L. Nelson and Michael M. Cox LEHNINGER PRINCIPLES OF BIOCHEMISTRY Sixth Edition CHAPTER 6 Enzymes © 2013 W. H. Freeman and Company

Name the reaction type and the coenzyme used

Binding of a substrate to an enzyme at the active site

There is an energy barrier between formation of product from substrate There is an activation energy formation of the transition state

Enzymes enhance reaction rates by lowering activation energies Enzymes do not affect equilibrium

How a catalyst circumvents unfavorable charge development during cleavage of an amide

Amino acids in general acid-base catalysis

Effect of substrate concentration on the initial velocity of an enzyme-catalyzed reaction Michaelis-Menten plot Double-reciprocal or Lineweaver-Burk plot

kcat = Vmax / [E]total kcat has units of reciprocal time

kcat / Km is a measure of catalytic efficiency

Many enzymes catalyze reactions with two or more substrates

Three types of reversible inhibition

Three types of reversible inhibition

Three types of reversible inhibition

Competitive inhibition Uncompetitive inhibition Mixed inhibition

Molecules that are transition state analogs are effective reversible competitive inhibitors

Irreversible enzyme inhibition

p. H – activity profiles for two enzymes

Structure of chymotrypsin, a serine protease

Mechanism of action of HIV protease

HIV protease inhibitors

The transpeptidase reaction

Mechanism of action of penicillin

Beta lactamase inactivates penicillin

Inactivation of beta lactamase by clavulanic acid

Subunit interactions in an allosteric enzyme, and interactions with inhibitors and activators

Aspartate transcarbamoylase, an allosteric enzyme

Regulation of enzyme activity by covalent modification

Regulation of enzyme activity by covalent modification

Regulation of enzyme activity by proteolytic cleavage Example: Activation of zymogens, inactive precursors of proteases