Chapter 12: Enzyme Kinematics pt. 2 Flashcards
Irreversible Inhibition
-inactivates/ destroys essential functional group on the enzyme by formation of a covalent bond
- can not be reversed
- does not have a steady state
Irreversible Inhibition: Group Specific Reagent
- DOES NOT resemble substrate
-inactivates enzyme by modifying essential R GROUP in active site - like to bond with Cysteine thiols
- EX: Hg and heavy metals (Pb, As, Ti)
-EX: Idoacetate (Idoacetamide), P-hydroxymercuribenzoate
Irreversible Inhibition: Affinity label for substrate Analog
- RESEMBLES substrate
- inhibits through REACTIVE Group binding at the active site (sim. to competitive inhibitor)
-EX: TPCK w/ HIS 57 of chymotrypsin
-EX: TLCK w/ HIS 57 of trypsin
Irreversible Inhibition: Suicide Inhibition
-also called suicide subtrates, mechanism-based inhibitors, trojan horse
- enzyme activates irreversible inhibitors that are inert/not reactive before activation
Characteristics:
- Inhibitor is inactive in the absence of E
- I activated to I* by target E
-once activated I* reacts w/ E
-EX: drug candidates due to minimal side effects
Bi Bi reactions
enzymatic reaction that involves 2 substrates which are neither transferase reactions or oxidation/reduction reactions
Bi Bi reactions: ordered sequential
seq. order which substrate binds
- 1S, 2S, then 1P, 2P
Bi Bi reactions: Random sequential
Does not matter which substrate binds first, but both S bind and then the products get released
Bi Bi reactions: Ping Pong ( double displacement mechanism)
- Substrate A, containing a functional group, binds to active site of the enzyme
- Enzyme takes functional group from substrate and gets modified to a stable enzyme intermediate
- Substrate A becomes P - Substrate P gets released
- Substrate B comes in and binds to the active site of the intermediate enzyme
- Intermediate Enzyme gives the functional group to Substrate B
- Substrate B becomes Q and then it leaves with the functional group
- Intermediate enzyme becomes a regular enzyme
*E is transiently covalently modified
Bi Bi reactions: Ping pong with LB plots
- More concentration of the substrate the close the linear line got to the x-axis
Vitamin: Pyridoxine
-vitamin B6
- Coenzyme: pyridoxal phosphate
- Rxn type: Amino group transfer or GABC
Aspartate Aminotransferase
-involved in amino acid catabolism (breakdown)
-have diff aminotransferase for diff aa
***mechanism S7
Control of enzyme activity: Control of the concentration of enzyme
-takes along time, hours/days
- Enzyme synthesis: regulation of transcription and translation
2.enzyme degradation: proteolysis
Control of enzyme activity: control enzyme activity
-protein-protein intermediate
- allosteric regualtion, noncovalent
- post-translational modification (carbohydrate tagging, proteolytic processing)
-reversible covalent modification
How to control enzyme activity?
- Control the concentration of enzyme
- control enzyme activity
Control of enzyme activity: Allosteric effect
if in T state:
-enzymatic activity decreases
-uses an allosteric inhibitor
if in R state:
-enzymatic activity increases
-uses an allosteric activator
-tend to have S shaped plots and non-linear LB plots
