Transcript Lehninger Principles of Biochemistry

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 for 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
pH – 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