Energi Kontraksi Otot

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Energi Kontraksi Otot

• dr. Susila Sastri M.Biomed
• Biokimia FK UNAND

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ATP

• Energy for the contracting muscle cell ATP
• ATP conc. in muscle cells 25 mmol/kg of dry
  skeletal muscle tissue,
• This amount is sufficient to keep muscles
  contracting at their maximal capacity for only a
  few seconds, thus active muscle cells must be
  able to recycle ADP to ATP to maintain
  contraction.

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Structure of ATP
adenosine triphosphate

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Function of ATP

• The contractile process.
• The pumping of calcium back into the sarcoplasmic
  reticulum during relaxation.
• Maintaining the sodium/potassium ion gradients
  across the sarcolema (membrane potential).

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Source of ATP

• Karbohidrat Glycolisis, TCA
• Fat Oxidation, TCA
• Protein Deamination, TCA
• The sarcoplasm of skeletal muscle large stores
  of glycogen, located in granules close to the I
  bands.
• The release of glucose from glycogen is dependent
  on a specific muscle glycogen phosphorylase ,
  which can be activated by Ca2, epinephrine, and
  AMP.

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Creating an H Gradient
OUTER COMPARTMENT
NADH
INNER COMPARTMENT
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Making ATP Chemiosmotic Model
ATP
INNER COMPARTMENT
ADPPi
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Pathways that provide for ATP synthesison
aerobic conditions

• Phosphocreatine.
• Glycolysis from Glycogen or Glucose.
• Tricarboxylic acid cycle (TCA or Krebs cycle).
• Electron transport chain.

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• If the need for contraction extends beyond a few
  seconds, fibres which require glucose as their
  fuel and energy source will begin to rely on
  hepatic gluconeogenesis to top-up their fuel
  supply and oxidative-type muscle fibres will
  increase their use of fatty acid to produce
  acetyl-coenzyme A for the TCA cycle.
• myocytes have enzyme-driven mechanisms which
  efficiently recycle ADP generated during
  contraction.

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• A key enzyme in the process of recycling lactate
  from muscle to liver is lactate dehydrogenase
  (LD) which catalyses the reversible
  interconversion of lactate and pyruvate.
• LD occurs in five isoenzymic forms and is
  widespread in cells around the body. The five
  isoenzymes arise due to the quaternary
  arrangement of the four subunits which comprise
  the enzyme. The subunits are of two types, H
  (heart) and M (muscle)

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Lactate dehydrogenase (LD)
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Isoenzymic forms of lactate dehydrogenase
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A. Energy metabolism in muscle fibers

• Red fibers (type I fibers) prolonged effort.
  Their metabolism is mainly aerobic and therefore
  depends on an adequate supply of O2.
• White fibers (type II fibers fast, strong
  contractions.
• These fibers are able to form sufficient ATP
  even when there is little O2 available, mainly
  obtain ATP from anaerobic glycolysis

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• Red fibers provide for their ATP
• fatty acids ß-oxidation
• tricarboxylic acid cycle
• respiratory chain
• The red color monomeric heme protein myoglobin,
  which they use as an O2 reserve.
• Myoglobin higher affinity for O2 than hemoglobin
  and therefore only releases its O2 when there is
  a severe drop in O2 partial pressure

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Regeneration of ATP

• Two enzymes, creatine kinase (CK) and adenylate
  kinase (AK), are important in this context
• Creatine and creatine kinase Creatine is
  synthesized from glycine and arginine and
  requires S-adenosyl methionine (SAM) as a methyl
  group donor.
• Creatine phosphate (also called phosphocreatine,
  PCr)
• a small compound which is a more energy rich
• able to rephosphorylate ADP so acts as an energy
  buffer

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Phosphocreatine (creatine phosphate / Pcr)

• Energy stored in the skeletal muscle.
• Creatine synthesized in the liver (from Arg,
  Gly, Met), and transported to the muscle cells,
  where it is phosphorylated by creatine kinase
  (ATP is required) to creatine phosphate.
• Serve as an ATP buffer in muscle metabolism.

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Creatine synthesis
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Creatine Kinase (CK)

• The enzyme responsible for this topping-up ATP
  in active muscle is CK.
• CK is found in high concentration in muscle cells
• isoenzyme CK-MM, CK-BB and CK-MB.
• predominant form in all muscles CK-MM, but
  cardiac muscle also contains a significant amount
  of CK-MB and this isoenzyme can be used as a
  specific marker of myocardial

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Adenylate kinase (AK)

• Whereas CK rephosphorylates ADP using PCr as the
  phosphate donor, AK (myokinase / AMP kinase)

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Fatty acid as a fuel in muscle

• Fatty acid oxidation occurs in mitochondria and
  peroxisomes in most tissues but quantitatively
  muscle is a major consumer of fat.
• fatty acids more calorific 38 kJ/mol,
  compared with 16 kJ/mol for glucose.

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Proteins and amino acids as fuels

• amino acids may be used as fuels during times
  when carbohydrate metabolism is compromised, for
  example, starvation or prolonged vigorous
  exercise.
• several different amino acids into intermediates
  of glycolysis (e.g. pyruvate) or the TCA cycle
  (e.g. oxaloacetate).

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• Alanine released from muscle protein or which has
  been synthesized from pyruvate via
  transamination, passes into the blood stream and
  is delivered to the liver.
• Transamination in the liver converts alanine back
  into pyruvate which is in turn used to synthesise
  glucose the glucose is exported to tissues via
  the blood. This is the glucose-alanine cycle

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Glucose-Alanin Cycle
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Recycling of ADP

• Muscle contraction produces ADP if this cannot
  be recycled to ATP contraction will cease.
• Rephosphorylation of ADP by mitochondrial
  oxidative phosphorylation is an obvious option
  for regenerating ATP, but this applies mainly to
  oxidative type I fibres.

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The multiple sources of ATP in muscle.
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• Sprinter Creatine Phosphate Anaerobic
  Glycolysis to make ATP.
• 100-m sprint creatine phosphate (first 45
  seconds) and then anaerobic glycolysis, using
  muscle glycogen as the source of glucose.
• Marathon Runner Uses Oxidative Phosphorylation
• The major fuel sources are blood glucose and free
  fatty acids, largely derived from the breakdown
  of triacylglycerols in adipose tissue, stimulated
  by epinephrine.