Enzyme Regulation Flashcards
Multiple steps in metabolic pathways allow
Efficient energy utilization
What do interconnections in metabolic pathways ensure?
Efficient utilization of metabolites
What are reversible reactions controlled by?
Changes in substrate
Irreversible reactions are…
Enzyme regulated
What is flux?
The rate at which the starting material is converted to the products of the pathway
What are 3 ways flux is controlled through a pathway?
- Enzymes in the pathway
- Supply of starting material
- Rate of product utilization
Flux through a pathway is never faster than what?
The rate limiting step
What is feedback regulation?
When the product of a pathway controls its synthesis
2 types of feedback regulation
- Product inhibition
- Feedback inhibition
List 5 factors involved in regulation of enzyme activity
- Substrate conc
- Product inhibition vs Feedback inhibition
- Allosteric activation and inhibition
- Cooperativity
- Post-translational modification
Phosphorylation/dephosphorylation
Proteolysis to activate an inactive precursor called
a zymogen
For many enzymes, where is [S]?
Near Km
When [S]»_space;Km, the rxn velocity…
Doesn’t change with [S]
When [S] «_space;Km, the rxn velocity…
Changes in proportion to [S]
According to the Michaelis-Menter Equation, how much change in substrate conc is necessary to access the full dynamic range of enzyme initial velocity?
~100 fold
What is product inhibition?
When the product of an enzyme inhibits that enzyme
What is feedback inhibition?
When the product of a metabolic pathway influences its production
What two isozymes are controlled by different mechanisms?
Hexokinase and glucokinase
Does hexokinase have high/low Km?
Low Km
What is hexokinase inhibited by?
Its product glucose-6-P
Does glucokinase have high/low Km?
High Km
What is glucokinase regulated by?
Conc of glucose, making it a “glucose sensor”
Whaat is allostery?
Process by which biological macromolecules transmit effect of binding at one site to an often distal, functional site, allowing for regulation of activity
What 2 things does allostery require?
- Binding
- Change in conformation associated with binding
What can allostery result in?
Activation or inhibition/positive or negative feedback
Allosteric enzymes have ___ and ___ affinity conformations
low and high
What does cooperativity apply to?
Multimeric enzymes En with n equivalent active sites
What are homotropic allosteric modifiers?
substrates for the active site
What are heterotropic allosteric modifiers?
Do not bind at active site; not substrates
Heterotropic allosteric modifiers differ from…
Ligand at active site
Heterotropic inhibitors stabilize a ___ affinity form of the active site
low
Heterotropic activators stabilize a ____ affinity form of the active site
high
What does PFK-1 do?
Incorporates phosphate from ATP into F6P to form F16BP
What shape is the graph of PFK-1 velocity vs F6P substrate?
Sigmoidal - signature of + cooperativity
PFK-1 has ___ identical subunits, each with 1 active site
4
In the absence of substrate F6P, PFK-1 exists in the ___-state
T
When F6P binds at 1 active site, all other sites…
Switch to high affinity R-state
F6P is a…
homotropic allosteric activator
ATP is what 2 things?
- Substrate
- Heterotropic inhibitor
PFK-1 has what 2 different ATP binding sites on each subunit?
- 1 ATP site is active site (where ATP is substrate)
- Other ATP site is not active site, it stabilizes low affinity T-state for F6P
F26BP is a….
Heterotropic activator
F26BP activates…
PFK-1
Where does F26BP not bind?
Active site of PFK-1/ Heterotropic allosteric activator
What enzymes do phosphorylation/dephos. and on what residues?
Kinases do phosphorylation/dephosphorylation of serine, threonine, or tyrosine residues
What enzymes do proteolysis that activate a precursor (zymogen/proenzyme)?
Proteases
Protein kinases transfer… to hydroxyl groups of…
Protein kinases transger phosphate from ATP (NTP) to hydroxyl groups of ser, thr, tyr
What do protein phosphatases do?
Remove phosphate from the enzyme
AMP is a …. of ….
AMP is a heterotropic allosteric activator of glycogen phosphorylase
High AMP in ___ cell
High AMP in a low energy cell
What further stabilizes glycogen phosphorylase active form?
Phosphorylation
Which of many enzymes are translated as inactive zymogens and activated by proteolysis?
Pancreatic digestive enzymes
What is the blood clotting cascade controlled by?
Proteolytic activation of inactive proteases (zymogens)
What converts prothrombin to thrombin?
Factor Xa
What is prothrombin?
An inactive protease (zymogen)
What is thrombin?
An active protease?
