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Energy Systems and Bioenergetics

Energy Systems and Bioenergetics. Energy systems and bioenergetics. Skeletal muscles, especially in elite athletes, can generate incredible work, during a marathon: Expend ~3000 Kcal, Oxidize >700 g CHO and >30 g fat Utilize >600 L oxygen, Break down and reform >150 mol ATP (63 kg)

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Energy Systems and Bioenergetics

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  1. Energy Systems and Bioenergetics

  2. Ex biochem c4-energetics Energy systems and bioenergetics • Skeletal muscles, especially in elite athletes, can generate incredible work, during a marathon: • Expend ~3000 Kcal, Oxidize >700 g CHO and >30 g fat • Utilize >600 L oxygen, Break down and reform >150 mol ATP (63 kg) • [ATP] in muscle very low • Skeletal muscle can suddenly increase rate of ATP use to > 100 times of rest • Myosin-actin cross-bridge • ~1/3 ATP hydrolyzed in contracting muscle is used in Ca2+ uptake by SERCA (sarcoplasmic-endoplasmic reticulum calcium ATPase) • <10% ATP hydrolyzed by Na+-K+-ATPase

  3. Ex biochem c4-energetics Overview of muscle contraction

  4. Ex biochem c4-energetics ATP utilization during exercise

  5. Ex biochem c4-energetics Myosin and muscle contraction • Myosin consists of 6 polypeptide chains • 2 myosin heavy chains (MHC), tail and head, form cross bridges with actin • 2 regulatory light chains, can be phosphorylated by accepting a Pi from ATP • 2 essential light chains • Myosin head also act as enzyme to hydrolyze ATP • Myosin ATPase • ATP + H2O  ADP + Pi

  6. Ex biochem c4-energetics Thick and thin filaments

  7. Ex biochem c4-energetics Myosin ATPase • By itself, myosin ATPase activity low, but increased by ~100 X when binds to actin • Actin-activated myosin ATPase, actomyosin ATPase • Different kinds of skeletal muscle MHC • Different ATPase activity, different rate of ATP hydrolysis, myosin isoenzymes (myosin isoforms, different molecular forms of same enzyme, catalyzed same reaction with different speed) • Human: MHC I, IIA, IIX • Smaller animals also have MHC IIB • Fast- and slow-twitch fibers • Muscle fibers have many nuclei, each express MHC genes: single muscle fiber may have >2 different MHCs

  8. Ex biochem c4-energetics

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  11. Ex biochem c4-energetics Histochemical Staining of Fiber Type Type IIa Type IIb Type I

  12. Ex biochem c4-energetics Energy-rich phosphates • ATP regeneration: ADP + Pi  ATP + H2O • Nucleotide: base + ribose + phosphate(s) • ATP: energy-rich compound • Anhydride bonds between alpha and beta phosphates, and beta and gamma phosphates • Analogy of a spring • In cell, [ATP]/[ADP] very high, ~500 • Ensure ATP hydrolysis • Muscle ATP utilization rate = regeneration rate in most exercise situations • Muscle [ATP] could decrease by 60-80% in very severe exercise, but very short-lived, replenished very rapidly soon after exercise

  13. Ex biochem c4-energetics ATP structure

  14. Ex biochem c4-energetics Nucleosides • Nucleoside:a compound that consists of D-ribose or 2-deoxy-D-ribose bonded to a nucleobase by a -N-glycosidic bond

  15. Ex biochem c4-energetics Nucleotide • Nucleotide: a nucleoside in which a molecule of phosphoric acid is esterified with an -OH of the monosaccharide, most commonly either the 3’-OH or the 5’-OH

  16. Ex biochem c4-energetics Phosphocreatine, creatine phosphate • [ATP] in most tissues low • 3-8 mmol/L cell water, 2-6 mmol/kg tissue • Energy turnover rate in muscle • 1 mmol ATP/kg/min at rest • 240 mmol/kg/min in sprinting in elite athletes, ~ 180 mmol/kg/min in normally active subjects • ATP in muscle consumed in ~ 2s if not regenerated • ATP regeneration rate < maximal ATP hydrolyzed rate • Sprint speed at maximal at start

  17. Ex biochem c4-energetics Phosphocreatine • ADP + PCr + H+ < ATP + Cr • Catalyzed by creatine kinase (very rich in muscle), fastest and most abundant among all muscle enzymes • Ensure ATP regeneration = break down near beginning of sprint-type activities • Act as temporary ATP buffer until other ATP-regenerating processes reach max rates • Forward direction in exercise, also consume H+ • Backward direction in recovery • [PCr] in muscle 18-20 mmol/kg • 92-96% PCr in human skeletal muscles • CK: MB isoenzyme in cardiac muscle, MM isoenzyme in skeletal muscle

  18. Ex biochem c4-energetics

  19. Ex biochem c4-energetics Energy systems • MgATP2- + H2O  MgADP- + n H2PO4- + (1-n) HPO4 2- + (1-n) H+ • All cellular ATP in cells associated to Mg2+ • ATP regeneration • PCr • Oxidative phosphorylation • Glycolysis • Only glycolysis in red blood cell (erythrocyte)

  20. Ex biochem c4-energetics Energy systems

  21. Ex biochem c4-energetics Oxidative phosphorylation • Aerobic system, aerobic metabolism, cellular respiration, respiration • Electrons transferred from substrate (CHO, fat)  carrier (NAD+, FAD+)  O2 • Measure disappearance of O2 as rate of oxidative phosphorylation • O2 consumption 1 L/min ~ 5 kcal/min • Can not quickly reach max rate because O2 transfer require time • Require 15-20s to double the rate • High capacity: large fuel tank

  22. Ex biochem c4-energetics Oxidative phosphorylation

  23. Ex biochem c4-energetics

  24. Ex biochem c4-energetics Glycolysis • Glucose + 2 ADP + 2 Pi + 2 NAD+  2 pyruvate + 2 ATP + 2 NADH + 2 H+ • Anaerobic glycolysis • Pyruvate + NADH + H+ < lactate + NAD+ • Catalyzed by lactate dehydrogenase (LDH) • Pyruvate can enter TCA cycle • Aerobic glycolysis • Net production of ATP from PCr and glycolysis: substrate-level phosphorylation

  25. Ex biochem c4-energetics Glycolysis and lactate • Glycolysis has higher activities than oxidative phosphorylation • Generate more pyruvate than TCA cycle can oxidize • Pyruvate converted to lactate, also regenerate NAD+ • Capacity of generating ATP: PCr < glycolysis < oxidative phosphorylation • ↓pH in very rapid rates of anaerobic glycolysis • Glycolysis can be quickly started at beginning exercise, reach max rate in 5-10 sec in intensive exercise

  26. Ex biochem c4-energetics PCr system, Anaerobic alactic system • ADP + PCr + H+> ATP + Cr • Consumption of H+ can be beneficial to muscle during high-intensity exercise • CK activity so high, can maintain ATP level remarkable well even during intense exercise • Low capacity: limited supply of PCr • [PCr] in muscle 18-20 mmol/kg, or 23-26 mmol/L • [PCr] can decrease >90% in all-out exercise • Regeneration of PCr during recovery by oxidative phosphorylation • Half-time for PCr recovery ~ 30 sec • Persons with higher capacity for oxidative ATP formation recovery PCr at faster rate • [PCr] and [TCr] Type II muscle fiber > Type I

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  30. Ex biochem c4-energetics PCr recovery after exercise

  31. Ex biochem c4-energetics Excess postexercise oxygen consumption (EPOC)

  32. Ex biochem c4-energetics Creatine supplementation • Increase [Cr], [PCr], [Total Cr] • PCr/TCr ratio in rested muscle constant at 0.6-0.7, even after supplementation • Most effective in short-term high-intensity exercise lasting up to 3 min in duration • Especially helpful if high-intensity activity is repeated with only brief recovery period • Increase body weight and strength gains along with resistance training • Allow to train harder • Upregulate expression of some genes in muscles, especially involved in intracullular signaling

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  35. Ex biochem c4-energetics Energy sources in different exercise intensities

  36. Ex biochem c4-energetics Energy sources in prolonged moderate-intensity exercise

  37. Ex biochem c4-energetics Energy source during maximal exercise with different durations

  38. Ex biochem c4-energetics Energy sources during repeated high-intensity exercise

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  42. Ex biochem c4-energetics

  43. Ex biochem c4-energetics Adenylate kinase, AMP deaminase • 2 ADP > ATP + AMP • Catalyzed by adenylate kinase (adenylyl kinase) • Prevent [ADP] accumulation, maintain high [ATP]/[ADP], ensure ATP hydrolysis • AMP + H2O  IMP + NH3 • AMP deaminase (adenylate deaminase) • NH4+ (ammonia) in blood • AMP deaminase activity higher in Type II fibers • Low at rest, activated by↓pH, ↑[ADP] • The 2 reactions maintain optimal energy status in muscle fiber during intense exercise • Irreversible AMP deaminase reaction drives reversible adenylate kinase reaction to the right • During recovery, IMP converted back to AMP, or form inosine and hypoxanthine

  44. Ex biochem c4-energetics Inosine

  45. Ex biochem c4-energetics Purine nucleotide cycle

  46. Ex biochem c4-energetics Purine nucleotide cycle

  47. Ex biochem c4-energetics Plasma lactate and NH3 after intensive ex

  48. Ex biochem c4-energetics Muscle metabolism in exercise • Techniques to measure muscle metabolism • Biopsy: invasive • Phosphorus 31 (31P) nuclear magnetic resonance (NMR) spectroscopy • Magnetic resonance imaging (MRI) • Identify ATP, PCr, Pi, estimate ADP, AMP • Expensive, limited type of exercise

  49. Ex biochem c4-energetics Identification of high-energy phosphate with 31P NMR Jung & Dietze, 1999

  50. Ex biochem c4-energetics 31P-NMR in PCr metabolism study Slade JM, 2007

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