1. Amino acid metabolism

2. proteins Only foodstuff that can form structures (tissues and enzymes) Made up of amino acids Protein synthesis, enzyme formation Can serve as fuel during long-term work 0.8 g/kg recommended for adults; probably too low for athletes

3. Protein structure: Amino acids Essential vs non-essential –Essential: NOT made by body –Non- essential: made by the body

4. Protein structure Carboxyl and amino termini come together to from protein structures (peptides) Amino acid

5. Digested in stomach and small intestine –Hydrocholoric acid (stomach) –Trypsin, chymotrypsin, carboxypeptidase (from pancreas) –Polypeptidases and dipeptidases in intestinal cells finish digestion Proteins in the diet

6. The amino acid pool –Free amino acids in the liver, skeletal muscle, plasma, interstitial fluid and intracellular water –All interconnected in that metabolism in one affects the others –Continuous excretion of nitrogenous end-products –Necessitates constant input of new amino acids –So, CONSTANT Protein turnover

7. Nitrogen balance Nitrogen is a component of AAs –Thus, used as a marker of protein metabolism Protein intake necessary to balance nitrogen turnover (input vs excretion) –0.8-1.0 g/kg is sufficient for most –1.2-1.6 g/kg is the highest recommendation for athletes

8. Removal of nitrogen Before amino acids can be used as fuel, nitrogen group must be removed Two ways –Deamination –Transamination Glutamate is a key player in both

9. Removal of Nitrogen Deamination –Occurs in liver 1) Requires NAD + as oxidizing agent 2) Produces ammonium ion 3) α-ketoglutarate can be used in Kreb’s cycle Called anaplerotic (to fill) addition to Kreb’s cycle 1 2 3

10. Removal of Nitrogen Transamination –Much more common –Transfers amine group from amino acid to keto acid SGPT and SGOT transaminases in liver AA Keto acid

11. Excretion of nitrogenous wastes Ammonia (small amt) Most is excreted as urea Urea cycle 1) Formation of carbamoyl phosphate from ammonia and Co 2 2) Addition of aspartate 3) Production of fumarate (Kreb’s cycle intermediate) 4) Produces Urea 1 2 4 3

12. Gluconeogenic amino acids Some amino acids used for gluconeogenesis 1)Pyruvate to OOA 2)OOA to PEP 3)PEP begins “reverse glycolysis” or gluconeogenesis So, amino acids that give rise to pyruvate and oxaloacetate –Can form phosphoenolpyruvate –Can be converted to glucose 1 2

13. Anaplerotic and cataplerotic reactions Anaplerotic (adding to) Cataplerotic (emptying) –These Rx add to or deplete the Kreb’s cycle Glutamate-glutamine Key intraorgan nitrogen transport vehicle, fuel source for GI tract and immune system and gluconeogenic precursor

14. Branched chain amino acids Leucine, Isoleucine and valine (LIV) Catabolized mostly in skeletal muscle Leucine: –Forms acetyl-CoA, acetoacetate and glutamate Leucine is thus called ketogenic Transamination

15. AA metabolism AA can be used in the following ways –Structural (proteins) –Anaplerotic additions to Kreb’s cycle This keeps the Kreb’s cycle working –Oxidized directly Branched chain AA –Other contributions to energetics Ketogenic –Produce ketone bodies when broken down Glucogenic –Contributes to gluconeogenesis

16. Glucose-alanine cycle Used during fasting Alanine can come from glycolysis or AA metabolism –Glycolysis Kreb’s cycle backs up during starvation –Pyruvate transaminated to alanine –Alanine converted to glucose in liver

17. Glucose- alanine II Other amino acids can also form alanine (glucogenic AA, anything that gives rise to pyruvate or OOA) So when Pyruvate builds up, converted to Alanine (1) Alanine shuttled to liver –Converted to glucose 1

18. Effects of endurance training on AA metab Greater rates of AA metabolism in trained subjects –Greater oxidation in human subjects during exercise

19. AA metabolism Note that leucine oxidation increases during exercise –This increases is linear with respect to exercise intensity –Particularly true in fasted state

20. Note that alanine appearance increases during exercise (1) and this can come from AA leucine (2) Also, glucose infusion reduces AA oxidation (3) AA metabolism 1 2 3

21. However, exercise training does not appear to increase AA metabolism in human subjects –If anything, it is reduced

22. Ammonia scavenging during high intensity exercise During high intensity exercise, AMP is formed –Adenylate kinase Rx ADP + ADP ATP + AMP AMP then inhibits AK Rx if it builds up AMP deaminated to IMP Muscle releases ammonia (NH 4 + ) during contraction –Contains nitrogen Purine nucleotide cycle

23. Ammonia scavenging Formation of glutamine (1) helps to transport ammonia in blood –Ammonia is toxic –Transamination Glutamine goes to kidney (2) Urea (3) and glucose formed (4) 1 2 3 4

24. Neuro-endocrine control of blood glucose

25. Hormones Chemical messengers –Produced and stored in a gland –Secreted into the blood –General and specific effects Two basic types –Steroid Produced from cholesterol by adrenal cortex and gonads –Polypeptides Amino acids

26. Hormones Powerful effects Precisely regulated –Feedback control (negative feedback) Mechanisms of action –Affect cell permeability (insulin) –Activate an enzyme (epinephrine) –Protein synthesis (GH)

27. Blood glucose homeostasis When fed –Liver glycogenolysis When fasted –Gluconeogenesis SNS helps in this –Epi stimulates liver glycogenolysis and gluconeogenesis Hormones –Released into blood –Epinephrine and nor-epinephrine

28. Maintenance of blood glucose levels is paramount –Fuel source –Anaplerotic additions to Kreb’s –Allows fat metabolism –Needed by brain and CNS Hormones that help maintain blood glucose –glucoregulatory Hepatic glucose production during exercise

29. Glucose homeostasis How difficult is this? Normal adult –Blood volume = 5L –Blood glucose = 100 mg/dl (1 g/L) –5g or 20 kcals (4kcal/g) worth of energy –Only enough to support 1 min of maximal activity! This means –We must get plenty of CHO prior to and even during activity –Liver supplements this

30. Glucose homeostasis Glucose production increased in 2 ways –Increased absorption from gut and liver output Liver glycogenlosis Liver gluconeogenesis

31. Glucose homeostasis Note how addition of arm exercise increases catecholamine levels –glucoregulatory hormone (raises blood glucose) Insulin falls –Decreases blood glucose Thus hormonal changes help maintain blood glucose levels Why increased?

32. Catecholamines and blood glucose Epinephrine and nor- epinephrine Epi binds to β-receptor –Activates adenylate cyclase –Muscle contraction increases intracellular Ca 2+ and Pi Stimulates glycogenolysis –Muscle and liver –Supports liver glucose production –Also increases lipolytic rate

33. Cyclic AMP Made from ATP (1) Intracellular messenger Activates many processes in metabolism Example –Glycogenolysis Epinephrine binds to receptor (2) Adenyl-cyclase creates cAMP (3) cAMP activates phosphorylase 1 2 EPI 3

34. Insulin and glucagon Insulin –β cells of the islets of langerhans of pancreas Glucagon –α cells Along with epinephrine and nor-epinephrine, main hormones of glucose homeostasis

35. Insulin response to exercise Falls in response to exercise –Epinephrine suppresses insulin secretion Thus –Glucose production is increased

36. Why insulin? Insulin –Helps facilitate glucose transport across sarcolemma during rest –Uses glucose transporters (GLUT) –GLUT-4 Insulin mobilizes transporters from intracellular pool Transporters move to sarcolemma

37. Glucose transport: exercise Muscular contraction –“insulin-like” effect –GLUT-4 can translocate due to insulin or Ca 2+ So, muscular contractions –Cause release of Ca 2+ –This causes translocation of Glut- 4 receptors –Important as epinephrine (released during exercise) inhibits insulin insulin

38. Neuro-endocrine control of hepatic glucose production Gluconeogenesis –Liver and kidneys 3 different enzymes than glycolysis –Pyruvate carboxylase –PEP carboxylase –Fructose 1,6 biphosphatase Glucose 6- phosphatase –Liver only So, muscle resynthesizes glycogen, liver and kidneys, glucose Pyruvate kinase

39. Gluconeogenesis Those 4 enzymes are either nonexistent or in small supply in skeletal muscle Found in large amts in liver and kidneys Pyruvate kinase (last step of glycolysis): –virtually irreversible in skeletal muscle –In liver, can be inhibited by cAMP and phosphorylation (Ca 2+ -dependent protein kinase) –Reduces glycogenloysis and promotes gluconeogenesis

40. Gluconeogenesis Pyruvate coverted to oxaloacetate (A) –High acetyl-CoA, low ADP Oxaloacetate converted to Phosphoenolpyruvate (B) –Low ADP Phosphoenolpyruvate converted to Fructose 1, 6 bisphosphate (C) F 1,6 bisphosphate converted to F6P (D) –High citrate, low AMP Converted to glucose (E) A B C D E

41. Hepatic glucose production The following hormones increase gluconeogenesis Inhibit pyruvate kinase –Glucagon –Epinephrine –Nor-epinephrine Insulin –Inhibits gluconeogenesis

42. Can muscle make glucose? Glycolytic muscle can produce glycogen from lactate –Glyconeogenesis Likely occurs early in recovery Muscle lacks G6 phosphatase –So can’t release glucose from cell However, it is possible that debranching enzyme can release glucose from glycogen –May help explain very rapid inc in blood glucose (fig 9-13)