Transcript Chapter 12 - Richsingiser.com

Fundamentals of
Biochemistry
Third Edition
Donald Voet • Judith G. Voet •
Charlotte W. Pratt
Chapter 11
Enzymatic Catalysis
Copyright © 2008 by John Wiley & Sons, Inc.
Section 4 – Lysozyme
NAG = N-acetylglucosamine
NAM = N-acetylmuramic acid
Non-polar environment
Glu – pKR = much higher
than 4.07
Asp – normal pKR = 3.09
Transition state analog
Covalent catalysis
Section 5 – Serine Proteases
• Highly reactive serine
• Many digestive enzymes use this
mechanism
• Inhibiting serine proteases can be very toxic
Identifying the active site residues
Serine was identified
by chemical labeling
His was identified by
affinity labeling
Trypsin with leupeptin inhibitor
Chymotrypsin
Elastase also have similar
Structures
Asp is very important
Catalytic triad
Asp, His, Ser
Substrate Specificity
Figure 11-30a
Figure 11-30b
Zymogens – inactive enzyme precursors
Fundamentals of
Biochemistry
Third Edition
Donald Voet • Judith G. Voet •
Charlotte W. Pratt
Chapter 12
Enzyme Kinetics, Inhibition, and Control
Copyright © 2008 by John Wiley & Sons, Inc.
Section 3 –
Control of
Enzyme
Activity
Allosteric regulation
T-state
R-state
Figure 12-13
Covalent Modifications
Phosphorylation is
most common
Ubiquitination
important for
protein
degradation
Glycogen Phosphorylase
Penicillin
• Penicillin – 1928 Alexander Fleming
• Disrupts synthesis of peptidoglycans by
transpeptidase
– Used for bacterial cell walls
• Lactam ring is highly reactive
Types of Penicillin
First, injection only
Acid stable, orally
Acid stable, orally
Most widely used
Mechanism of Penicillin
Bacterial Evolution
Bacterial now produce an
enzyme lactamase
Inactivates penicillin
Human response
Create inhibitor of β-lactamase
Clavulanic acid
Augmentin – combination of
both amoxicillin and clavulanic
acid
New bateria resistant to both
The battle continues…..
HIV
• Retrovirus – RNA genome
• Make a polyprotein consisting of 3 proteins
– Reverse transcriptase, integrase, protease
– Drugs for all enzymes
– Drugs for attachment
Protease mechanisms
•
•
•
•
Serine proteases (chymotrypsin)
Cysteine proteases
Aspartyl proteases (HIV protease)
Metalloproteases
HIV protease mechanism
HIV protease inhibitors
OH – mimics stable intermediate, benzene ring mimics
hydrophobic aa
Other HIV drug targets
• Integrase inhibitors
– FDA approved in 2007 (raltegravir)
– Inhibits strand transfer of viral DNA into host
genome
• Reverse Transcriptase Inhibitors
– AZT 1987
– Nucleoside inhibitors (terminate DNA chain)
– Non-nucleoside inhibitors (irreveribily bind to RT)
• Coming soon…
– Viral fusion, maturation
HIV
T-cell – green
HIV – red