Allosteric enzymes

Question 1

what are allosteric enzymes regulated by?

Answer 1

• can be positive or negatively effected
• regulated by effector molecules (allosteric activator or inhibitor)

Question 2

effector

Answer 2

ions binding at another site (allosteric site) which causes a conformational change, to make activity better or worse.

Question 3

The idea of inhibition and activation refers to…

Answer 3

populations of molecules.
When talking about allosteric activation talking about activating a subset of the population…

Question 4

homoallostery vs heteroallostery

Answer 4

homo - same moelcule or ion as is used in chemical reaction

hetero- something that is different.

ex: hemoglobin binding Oxygen is affected by oxygen binding, therefore is homoallosteric

Question 5

symmetrical model

Answer 5

(MWC).
symmetrical (protein quaternary structure must be symmetrical such as c2, d4 etc) homo-oligomers (protomeric units are the same… same sets etc) and a concerted (Sn2, diels alder SINGLE mechanism step) conformational change.

KEEPS symmetry during conformational change.

Ligand free oligomers are in 2 states (4 structure, T or R) at equilibrium. These will shift when a ligand binds to the first state, and that change in conformation changes the ligand affinity

Question 6

T and R states

Answer 6

these are quaternary structures.
T = tight, not efficient
R = relaxed, ligand bound, efficient

Question 7

Sequential model

Answer 7

KNF
- ligand bound to 1 subunit causes a conformational change in a different subunit, which allows better ligand binding in that spot
- if conformation changes because i bound a ligand, it means ligand binds better.
- can have HYBRID states.

Question 8

R and T states

Answer 8

At low substrate concentration, the quarternary structure of E is mostly in its T state. This means that the subunits are in close proximity and create a compact and constrained structure, which prevents high affinity to substrate, and prevents high catalytic activity.

As [S] rises, substrate molecules begin to bind to active sites, which begins to shift equilibrium towards the R state. The R state means that there has been a change in conformation, and decreases constrain in the 4 structure. This increases the active sites affinity for substrate and activity of the enzyme (more product created?)

Due to homeostasis, there is constant equilibrium shifting.

Question 9

What does KNF binding depend on?

Answer 9

the number of ligands bound, NOT the quaternary structure.

Question 10

KNF is an adaptation of…

Answer 10

the induced fit model.

Question 11

population shift

Answer 11

Conformation selection…. substrate selects a conformation whose binding site is most complementary to the E… selects a conformation that resembles if ES was present.

Once that selection has occurred, then that conformation will be stabilized, which means you are shifting the equilibrium to favor that conformation.

this means the enzyme will either be more active or more inhibited.

Question 12

Morpheein

Answer 12

morphs of a protein (shape)…
- changing the oligomeric state of the protein.
- dissociation of a higher order multimer into lower order multimer.

• conformational change occurs in the lower order state prior to assembly of an alternate higher order multimer.
  During this process, allosteric effector can bind to the lower order multimer and shift the equilibrium (through KNf, WMC, etc) to the lower order, which allows for assembly into a higher ordder.

higher order may be active form!

Question 13

cooperativity

Answer 13

when enzymes or receptors with multiple binding sites have 1 binding site bind a ligand, which then affects the affinity of other sites for a ligand… this can either be positive or negative

Question 14

physiological function of sigmoidal kinetics

Answer 14

S shaped graph.
- we are doing this because we want to enhance substrate level control (S or P directly bind to E to either A or I) so that the rate oscillated around the [S] critical
why? [S]critical is where the enzyme functions best
- oscillates by enzyme being fed more substrate then less substrate

Question 15

When [S] is low, the enzyme is mostly in the T state. Why?

Answer 15

• dont have a lot of [S], mostly going to be in T state because not a lot of substrate to cause the enzyme to change into the R state (MAYBE)
• think about it more lfrom the perspective of the effector. Why keep enzyme in T state uding ASI when there is low [S]?
• if [S] gets too low, no longer in the [S]crit zone, and using an ASA to change the enzyme into the R state will decrease the levels of free [S], which will completely remove you from [S]crit

Question 16

When [S] is high, enzyme is mostly in the R state, why

Answer 16

The enzyme shoudl be kept in the R state by an ASA if substrate levels are high, because this will increase the amount of substrate moving to product, which decreases the levels of substrate concentration. This is ideal to keep the amount of free substrate in the [s]critical zone