L10- Enzyme regulation and inhibition Flashcards
What are th stereoisomers of amino acids?
The NH3 is on the left- L
NH3 is on the right- D
The R and coo- group must be going away from you and the H and Nh3+ groups must be coming towards you. Like in the sugars
Nh3+ on left= L
Nh3+ on right= D
What kind of enzymes are jey metabolic control enzymes usually?
Allosteric
What atructure do most allosteric enzymes have?
Quaternary structure
With “cooperativity” between their subunits
Apart from the active site, what do noncovalent allosteric enzymes have?
A secondary regulatory site (allosteric site) distinct from the active site.
Allosteric inhibitors or activators bind to this site and regulate enzyme activity via conformational changes. - noncovalent allosteric regulation.
What is cooperativity?
Binding by a substrate to one active site affects subsequent binding to all other subunits. (to more active form usually)
Due to subunit cooperativity, what shape are rate versus substrate conc. plots?
Sigmoidal
What forms does an allosteric enzyme have?
Active form - R form
Inactive form - T form
What do activators and inhibitors do to enzymes?
- Binding of activators stabilizes the active form (R form)
- Binding of inhibitor stabilizes the inactive form (T form) of the enzyme.
What is PFK-1?
An allosteric enzyme which catalyses the early step in glycolysis. Turns fructose-6-phosphate into fructose-1,6-biphosphate.
What are allosteric activators and inhibitors of PFK-1?
AMP= activator
PEP= inhibitor. PEP is produced later in glycolysis so acts– feedback inhibition
What do AMP and PEP affect the Km of PFK-1?
AMP- lowers km. For a given concentration of fructose-6-phosphate, intial rate is higher.
PEP- increases Km.
What does a high [pep]/[amp] ratio cause?
Higher Km
Lower PFK-1 activity
Less glycolysis
What are the 3 types of inhibitors?
Competitive- competes for binding site
Noncompetitive- binds to ES complex or enzyme site.
Uncompetive- binds to ES complex
How does each inhibitor affect vmax and Km?
Competitive- vmax unchanged, km increased
Uncompetitive- vmax decreased, km also decreased, slope the same so lines parallel
Non-competitive- vmax reduced, km unchanged
In the lineweaver-burk plots what will each inhibitor look like?
Competitive- will intersect on 1/Vo axis (y axis) because vmax isn’t changes.
Uncompetitive- will have parallel lines because vmax and km are reduced.
-Non-competitive- the lines will intersect on the 1/[s] x-axis because the km does not change
