Application of Carbohydrate Metabolism Review of Allosteric sites Futile Cycling Insulin and Glucagon Amino Sugars

Lactate Lactate Lactate Lactate Glucose Glucose Glucose Glucose J = 0 VF > VR VF < VR Rate-controlling Step Rate-controlling Step Rate-controlling Step Rate-controlling Step Lactate Lactate Lactate Lactate

Adenylate kinase Rule: the balance of ATP, ADP, and AMP in a cell is controlled by adenylate kinase. Reactions that elevate ADP elevate AMP, a major allosteric regulator. Equation K = [ATP][AMP] [ADP]2 2ADP ATP + AMP Biological Reality 100 ATP 10 2 ADP AMP Rule: A small change in ATP will have a strongly magnifying effect on ADP or AMP concentrations in the cell

ATP ATP Examples in Working Muscle ADP K = [ATP][AMP] [ADP]2 ADP 100 0.1 mM 1 mM 0.02 mM If ATP concentration drops by 10%, adenylate kinase will readjust the levels of ADP and AMP to compensate 100% -10% >400% ATP ADP AMP 0.2 mM 0.9 mM ~0.1 mM

Key ALLOSTERIC Regulatory Points GLYCOLYSIS-GLUCONEOGENESIS Glucose G6P HK G6Ptase -Citrate F6P FBP PFK-1 F6BPtase -ATP +AMP +F2,6P -AMP -F2,6P PEP PYR PK -Alanine +F1,6BP PYR OAA PC +Acetyl-CoA OAA PEP PEPCK +Glucagon, cAMP F6P F2,6P PFK-2 FBPase-2 -Citrate +AMP -F6P -ATP No Allostery

Fructose-2,6-Bisphosphate A Major Allosteric Regulator Synthesized by Phosphofructokinase-2 Destroyed by Fructose-2,6-Bisphosphatase Powerful Activator of Glycolysis Powerful Inhibitor of Gluconeogenesis Not an Intermediate in any Pathway

O O O3POCH2 OH Fructose-6-P Fructose-1,6BP PO3= CH2OH 6 2 OH CH2OH -D-Fructose-2,6BP 1

Fructose 2,6 Bisphosphate STIMULATES GLYCOLYSIS INHIBITS GLUCONEOGENESIS

Fructose-2,6-bisPO4 (F2,6BP) the most important allosteric effector that regulates glycolysis-gluconeogenesis Activates PFK-1 Inhibits F1,6-bisPtase F2,6BP level controlled by rates of synthesis and degradation F6P F2,6BP PFK-2 Both in Same Protein FBPtase-2 F6P F2,6BP (-)Citrate (-)F6P (+)AMP (+)Glycerol-3-PO4 PFK-2 FBP-2 (+)F6P Glycolysis Gluconeogenesis

Hormonal Control of F2,6BP See P. 458 Hormonal Control of F2,6BP Glucagon Epinephrine Liver cAPK cAMP PFK2 (a) PFK2 (b) FBPase2 (b) FBPase2 (a) ATP ADP P cAPK Kinase Phosphatase Inhibits glycolysis Stimulates gluconeogenesis cAMP IN LIVER: cAMP activates the phosphatase that destroys F2,6BP and inhibits the kinase that makes F2,6BP. The combined effect is to stimulate gluconeogenesis in liver.

FUTILE CYCLING F6P PO4 H20 ATP ADP F1,6BP At steady-state, net reaction is: ATP + H2O ADP + PO4 TAKE HOME: To prevent futile cycling, rates of synthesis and degradation in an ATP-dependent step must not be the same.

INSULIN VS GLUCAGON See Page 686 in Textbook Insulin: Stimulates Glycolysis, Glycogen Synthesis Insulin is designed to remove blood glucose and allow cells to metabolized the glucose or make glycogen Insulin inhibits gluconeogenesis Glucagon: Promotes Gluconeogenesis, Glycogen Breakdown Glucagon is designed to raise blood glucose and assist liver in controlling blood glucose levels Elevates cAMP in liver and stimulates protein phosphorylation Targets: PEPCK Glycogen Synthase FBPtase-2 PK Glycogen Phosphorylase

Amino Sugars Synthesized from D-fructose Amine group donated by glutamine Acetylated Found in GAGS, proteoglycans and glycoproteins Examples are N-acetylglucosamine, N-acetylgalactosamine, N-acetylneuraminic acid (Sialic acid)

Amidotransferase AMINO SUGARS 2nd C CH2OH C=O HO-C CH2OP C-OH F-6-P COO- C-H CH2 C-NH2 L-Glutamine H3N- O CHO C-NH3 HO-C CH2OP C-OH H- + D-Glucosamine CHO C-N HO-C CH2OP C-OH H- Amidotransferase -C-CH3 O Acetyl-CoA N-Acetyl-D-glucosamine

3-Stages of Glycoprotein Synthesis Assembly of oligosaccharide chains on Dolichol Assembly of polypeptide chain with Asn-X-Ser/Thr on ribosomes Final tailoring of oligosaccharide chains in Golgi Finished product for secretion or intracellular targeting

Energy in Glucose (Aerobic) Glucose F1,6BP: -2 ATP F1,6BP 2 Pyr: 4 ATP 2 NADH 6 ATP Mitochondria 2Pyr 2Acetyl-CoA: 2NADH = 6 ATP 2Acetyl-CoA 4CO2 24 ATP 38 ATP C6H12O6 + 6O2 6CO2 + 6H2O Go’= -2,850 kJ/mol Conserved = 38 ATP x 30.5 kJ/ATP = 1,159 kJ Efficiency = 40.7%

Energy in Succinate Succinate Fumarate: 1 FADH2 = 2 ATP Fumarate Malate: 0 Malate OAA: 1 NADH = 3 ATP OAA 4CO2: 2 cycles = 24 ATP Total = 29 ATP

Succinate C4H6O4 3½ O2 4CO2 + 3H2O + Glucose C6H12O6 + 6O2 6CO2 + 6H2O COOH CH2 + 3½ O2 4CO2 + 3H2O C4H6O4 Glucose CHO CH2OH HO-C-H H-C-OH C6H12O6 + 6O2 6CO2 + 6H2O