Regulation of Metabolism

Chapter -15

Lehninger

Principles ofBiochemistry5th edition

Nelson & Cox

http://www.genome.ad.jp/kegg/pathway/map/map01100.html

Regulation of Metabolism

• Cells dynamic steady state.

• Regulatory mechanism evolved under strong __________ pressure.

• Regulatory enzyme respond to changes in _____________ concentration.

• Enzyme can be ________ in several ways.

Factors affecting the activity of enzymes.

• _______ a phosphoryl group from ATP to a Ser, Thr, or Tyr residue in an enzyme or other protein substrate.

• Protein phosphatases __________ the phosphoryl group as Pi.

Protein phosphorylation and dephosphorylation.

Role of AMP-activated protein kinase (AMPK) in carbohydrate and fat metabolism

Regulation of Glycolysis

• Catalyzes _____ of glucose into Glycolysis

• ___________ enzyme

• 4 Isozymes (I-IV)

Regulation of Glycolysis:

Hexokinase

• Muscle hexokinase I and II are allosterically _________ by higher levels of their product glucose 6-phosphate.

Isozymes are temporarily and reversibly inhibited to keep a balance with utilization.

Regulation of Glycolysis:

Hexokinase II

• myocytes (muscle cell) • ________ affinity for glucose (half saturated at 0.1mM)• Glucose entering myocyte has a concentration of _______mM - Hexokinase II to work at maximum rate.

http://bio.winona.edu/berg/ANIMTNS/allostan.gif

Allosteric regulation

Hexokinase IV (Glucokinase) Liver isozyme: Its different

1. Its 1/2 saturation reaches at _____mM of Glucose. (above normal blood glucose level)

Excess glucose (after meal) is transported to ___________ where hexokinase IV converts it into Glucose 6-phosphate.

2. Specifically _________ by a binding of a regulatory protein in liver.

Regulation of Glycolysis

• Tighter binding by regulatory protein in presence of Fructose 6-Phosphate.

• While ______________ levels of glucose relieves this binding/ inhibition.

• Low blood glucose level (<5mM) (Fasting), Fructose 6-P triggers inhibition of _____________ via binding of the regulatory protein.

Ensures that liver _______ compete with other organs for the glucose.

Regulation of Glycolysis: Hexokinase IV

Regulatory Protein anchors Hexokinase IV inside _________, away from cytosolic enzymes of ______________.

Higher glucose levels in cell leads to higher level in nucleus and results into release Hexokinase IV from regulatory protein allowing it to enter cytosol.

Hexokinase IV is not ____________ by the higher levels of Glucose 6-Phosphate and continue to operate while Hexokinase I-III are inhibited.

Regulation of Glycolysis: Hexokinase IV

nucleus

glycolysis

• _____ binds PFK-1 at an allosteric site & inhibits it by lowering its affinity for Fructose 6-Phosphate.

• While ADP & AMP ________ this inhibition by ATP.

Regulation of Glycolysis:

PFK 1: Allosterically regulated

- Higher conc. of _____ enhances inhibition by ATP. (Tells system that glucose need not to be utilized for ATP generation)

- Fructose 2,6-bisphosphate is allosteric _________ of PFK-1. (different from Fructose 1,6 bisphosphate)

Regulation of Glycolysis

More regulation of PFK1

Regulation of Glycolysis:

Pyruvate Kinase

- 3 isozymes: all _______ by high concentrations of - ATP, Acetyl-CoA and long-chain fatty acids.

- Liver (L) form of PK: regulated by phosphorylation.

Regulation of Glycolysis:

Pyruvate Kinase

- Several steps are __________.

- Acetyl-CoA _____ the formation of oxaloacetate.

- Inhibits pyruvate dehydrogenase complex. Pyruvate

Regulation of Gluconeogenesis

- FBPase-1 is inhibited strongly by _______ - while the _______ is activated.

Coordinated regulation of both pathways in a reciprocal manner.

Regulation of Gluconeogenesis

Gluconeogenesis

• Besides these allosteric regulation inside cell.

• There could also be hormonal regulation from ___________ of cell:

Insulin (51 aa), glucagon (29 aa) etc.

Hormonal

Regulation of Gluconeogenesis

Both Glycolysis and Gluconeogenesis

levels of Glucagon in the events of lower blood glucose levels signals liver to: - produce and release more glucose and - Stop using it.

This is mediated by Fructose 2,6-bisphosphate which is ______________regulator of : PFK-1 and FBPase-1

Fructose 2,6-bisphosphate mediated regulation

• Without Fructose 2,6BP binding PFK-1 is virtually ______.

• Its binding stimulates glycolysis and at the same time _______ FBPase-1 to slow down gluconeogenesis.

Fructose 2,6-bisphosphate mediated regulation

Fructose 2,6-bisphosphate mediated regulation The cellular levels of F2,6-BP reflects levels of ________ in the blood:

-Glucagon with in ________ level.

F2,6-BP levels: Controlled by its formation and breakdown.

F2,6-BP formed by phosphorylation of Fructose 6-P, catalyzed by __________ and broken by FBPase-2. (both are different from PFK-1 & FBPase-1)

PFK-2 and FBPase-2 are two distinct activities of the _______ bifunctional protein: - regulated by ___________ and __________.

Fructose 2,6-bisphosphate mediated regulation

Glucagon lowers the F2,6-BP levels: - inhibits glycolysis and _________ gluconeogenesis.

Fructose 2,6-bisphosphate mediated regulation

Insulin increases the F2,6-BP levels: - Stimulating glycolysis and __________ gluconeogenesis.