Enzyme Regulation of Enzyme Activity | Biochemistry for MCAT PDF Download

 Page 1


Chapter 5 (part 4)
Enzyme Regulation
Page 2


Chapter 5 (part 4)
Enzyme Regulation
Regulation of Enzyme Activity
Enzyme quantity – regulation of gene expression (Response time = 
minutes to hours)
a) Transcription
b) Translation
c) Enzyme turnover
Enzyme activity (rapid response time = fraction of seconds)
a) Allosteric regulation
b) Covalent modification
c) Association-d i s a s s o c i ati o n ’
d) Proteolytic cleavage of proenzyme
Page 3


Chapter 5 (part 4)
Enzyme Regulation
Regulation of Enzyme Activity
Enzyme quantity – regulation of gene expression (Response time = 
minutes to hours)
a) Transcription
b) Translation
c) Enzyme turnover
Enzyme activity (rapid response time = fraction of seconds)
a) Allosteric regulation
b) Covalent modification
c) Association-d i s a s s o c i ati o n ’
d) Proteolytic cleavage of proenzyme
Allosteric Regulation
• End products are often inhibitors
• Allosteric modulators bind to site other 
than the active site
• Allosteric enzymes usually have 4
o
structure
• Vo vs [S] plots give sigmoidal curve for 
at least one substrate
• Can remove allosteric site without 
effecting enzymatic action
Page 4


Chapter 5 (part 4)
Enzyme Regulation
Regulation of Enzyme Activity
Enzyme quantity – regulation of gene expression (Response time = 
minutes to hours)
a) Transcription
b) Translation
c) Enzyme turnover
Enzyme activity (rapid response time = fraction of seconds)
a) Allosteric regulation
b) Covalent modification
c) Association-d i s a s s o c i ati o n ’
d) Proteolytic cleavage of proenzyme
Allosteric Regulation
• End products are often inhibitors
• Allosteric modulators bind to site other 
than the active site
• Allosteric enzymes usually have 4
o
structure
• Vo vs [S] plots give sigmoidal curve for 
at least one substrate
• Can remove allosteric site without 
effecting enzymatic action
Regulation of Enzyme Activity
(biochemical regulation) 
• 1
st
committed step of a biosynthetic pathway or 
enzymes at pathway branch points often regulated 
by feedback inhibition.
• Efficient use of biosynthetic precursors and 
energy
B A C
1
3”
3’
2
E F G
4’
5’
H I J
4”
5”
X
X
Page 5


Chapter 5 (part 4)
Enzyme Regulation
Regulation of Enzyme Activity
Enzyme quantity – regulation of gene expression (Response time = 
minutes to hours)
a) Transcription
b) Translation
c) Enzyme turnover
Enzyme activity (rapid response time = fraction of seconds)
a) Allosteric regulation
b) Covalent modification
c) Association-d i s a s s o c i ati o n ’
d) Proteolytic cleavage of proenzyme
Allosteric Regulation
• End products are often inhibitors
• Allosteric modulators bind to site other 
than the active site
• Allosteric enzymes usually have 4
o
structure
• Vo vs [S] plots give sigmoidal curve for 
at least one substrate
• Can remove allosteric site without 
effecting enzymatic action
Regulation of Enzyme Activity
(biochemical regulation) 
• 1
st
committed step of a biosynthetic pathway or 
enzymes at pathway branch points often regulated 
by feedback inhibition.
• Efficient use of biosynthetic precursors and 
energy
B A C
1
3”
3’
2
E F G
4’
5’
H I J
4”
5”
X
X
Phosphofructokinase( PFK)
Fructose-6-P + ATP -----> Fructose-1,6-bisphosphate + ADP
•PFK catalyzes 1
st
committed step in glycolysis (10 steps 
total)
(Glucose + 2ADP + 2 NAD
+
+ 2Pi ? 2pyruvate + 2ATP + 2NADH)
•Phosphoenolpyruvate is an allosteric inhibitor of PFK
•ADP is an allosteric activator of PFK