REGULATION OF METABOLISM

REGULATION OF METABOLISM

(A) Non Hormonal regulation

(i) Allosteric control:

• The activity of the key metabolic enzymes in the pathway is modulated by the level as activators or inhibitors of metabolites that act.

• In Glycolysis, phosphofructokinase is activated by fructose-2,6 bisphosphate and AMP and inhibited by citrate and ATP.

(ii) Respiratory control:

• Pathways are regulated in this manner are TCA cycle, B-oxidation, and oxidative phosphorylation.

(iii) Covalent modification:

• Covalent modification of the key enzyme of a pathway is used to regulate the pathways. In glycogenesis, glycogen synthase is inactive when phosphorylated and active when dephosphorylated.

 • In glycogenolysis, glycogen phosphorylase is active when phosphorylated and inactive when dephosphorylated

(iv) Substrate availability:

• Substrate availability is primarily determines

the flux of metabolites through the following allied

•Pentose phosphate pathway

• Urea cycle

(B) Hormonal regulation

(i) Insulin signals the fed state.

• Insulin stimulates the synthesis of glycogen, fat, and protein. • Insulin inhibits the degradation of glycogen, fat, and protein.

(ii) Glucagon and epinephrine signal the fasting state.

 • Glucagon and epinephrine inhibit the synthesis of glycogen, fat, and protein.

Glucagon and epinephrine stimulate the degradation of glycogen, fat, and protein. Epinephrine also signals stressful states when the mobilization of fuel is required.