Regulation of Glycolysis

Question 1

How do you control flux?

Answer 1

1. Identify rate-determining step/s (measuring ∆G in vivo)
2. Identification of allosteric modifiers of enzymes in step 1 in vitro
3. Measurement of in vivo levels of identified modifiers in step 2

Question 2

In controlling flux, how do you identify the rate-determining steps (rds)? What are important reminders?

Answer 2

rds have very negative ∆G

last step is rarely regulated as this is a waste of energy
if a step has multiple sources, it is rarely regulated as the product can be synthesized from many sources.

Question 3

Reminders when doing in vitro identification of allosteric modifiers?

Answer 3

allosteric modifiers can be the substrate itself or the product

Question 4

In controlling flux through PFK 1, how does the addition of ATP affect the mechanism?

Answer 4

Addition of ATP will result in it acting as in inhibitor, reducing enzyme activity

Question 5

In controlling flux through PFK 1, what will never exceed 10% even if demand for this changes?

Answer 5

change in concentration of ATP

Question 6

What can counter the effects of ATP? How?

Answer 6

AMP and ADP counters by enhancing the activity of the enzyme

Question 7

How does ADP and AMP get involved in reactions in muscle cells?

Answer 7

2 ADP produces 1 ATP + 1 AMP catalyzed by adenylate kinase to help supply extra ATP

ATP + creatine produces phosphocreatine + ADP catalyzed by phosphoprotein kinase

Question 8

What is a relationship regarding the concentrations of ATP, AMP, and ADP?

Answer 8

10% decrease in [ATP], 100% increase in [ADP], 400% increase in [AMP]

Question 9

What are the two states of PFK? Differentiate.

Answer 9

T-state is the inactive form which has a low affinity for substrates (dephosphorylated)

R-state is the active form which has a high affinity for substrates (phosphorylated)

Question 10

AMP binding causes..?

Answer 10

shift to R-state as AMP is an allosteric enhancer. It also has stabilizing effect of substrate on the active site

Question 11

ATP binding causes..?

Answer 11

Shift to T-state as ATP is an allosteric inhibitor. It is countered by Ser residue but Ser residue is countered by glucose.

Question 12

Why is PFK and FBPase catalyzed reactions considered a futile cycle?

Answer 12

No synthesis of usable products but consumes ATP. Only for regulation.

Question 13

If AMP enhances PFK, what does it do to FBPase?

Answer 13

inhibit

Question 14

Describe nonshivering thermogenesis

Answer 14

releasing heat through substrate cycling e.g. ATP hydrolysis releases heat