BC basic - from big bang

1
Allosteric Enzyme ATCase
Active relaxed form
Aspartate
Carbamoyl phosphate
Carbamoyl aspartate

ATCase
Quaternary structure
CCC
Catalytic subunits
R R
R R
R R
Regulatory subunits
CCC
Catalytic subunits
Inactive tense form
Juang RH (2004) BCbasics
2
Sigmoidal Curve Effect
vo
Noncooperative (Hyperbolic)
Positive effector (ATP) brings sigmoidal
curve back to hyperbolic Negative effector
(CTP) keeps
Sigmoidal curve
Cooperative (Sigmoidal)
Exaggeration of sigmoidal curve yields a
drastic zigzag line that shows the On/Off
point clearly
Consequently, Allosteric enzyme can sense the
concentration of the environment and adjust
its activity
Off
On
Substrate
Juang RH (2004) BCbasics
3
Mechanism and Example of Allosteric Effect
Allosteric site
R Relax (active)
Homotropic () Concerted
Allosteric site
A
Heterotropic () Sequential
X
T Tense (inactive)
I
Heterotropic (-) Concerted
X
X
Juang RH (2004) BCbasics
4
Activity Regulation of Glycogen Phosphorylase
Covalent modification
GP kinase
P
T
T
P
GP phosphatase 1
Non-covalent
ATP Glc-6-P Glucose Caffeine
spontaneously
A
Glucose Caffeine
AMP
Garrett Grisham (1999) Biochemistry (2e) p.679
A
R
R
A