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Purine nucleotides and phosphocreatine
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Free energy ΔG = ΔH – TΔS ΔG G=free energy H= enthalpy (heat energy)
T= temperature S=entropy ΔG Difference in free energy between the reactants and the products When direction of Rx is as follows ATP→ ADP + Pi ΔG is negative Because we are losing usuable energy
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ATP and PCr Free energy released from the breakdown of CHO and fats
Stored in “high-energy” phosphates ATP, PCr Enzymes break down both these compounds to: ATP: perform cellular work ATP↔ADP + Pi ATPase (ATP kinase) PCr: resynthesize ATP PCr +ADP↔ATP+Cr Creatine kinase Can also use the ADP ADP + ADP ↔ ATP + AMP Adenylate kinase
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ATP ATP Adenine, ribose and 3 phosphate groups
Used for almost all energy requiring reactions in the body Large change in free energy when Pi is cleaved by ATPase Enough stored to fuel ~2s of maximal effort Why don’t ATP levels fall? PCr Acts as temporal (filling the time until mitochondria comes fully online) buffer of ATP concentrations
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ATP & PCr PCr ~3-4 times as much as ATP
So, now we have ~8s of maximal activity PCr + ADP ↔ ATP + Cr This reaction occurs faster than the ATPase reaction Thus, ATP does not fall Cr and PCr are more mobile within the cell than ATP Thus, may also act as a spatial buffer of ATP concentrations
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ATP and PCr in recovery from work
Note how PCr falls and recovers with about the same rate Time constant: ~30-60s PCr recovery is dependent upon Oxygen delivery pH ATP+Cr ↔ ADP + PCr + H+ Note how resynthesis of PCr acidifies the cell
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Muscle adenylate pool Energy charge=
Indication of the energy status of the cell Ability to perform work Energy charge at rest Close to 1 Typically, Energy charge at complete exhaustion Close to 0.75
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Adenylate pool Changes in the energy charge
Dictate how fast ATP resynthesis occurs Lower energy charge, faster ATP resynthesis (1) Accelerates all ATP providing Rx If energy charge gets low enough (2) Fatigue Rate of ATP production and utilization Same where lines intersect Note that energy charge is usu above this level Increased ADP, AMP and Pi stimulate ATP production Increased ATP inhibits these Rx 1 2
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Adenine nucleotide loss
ATP, ADP, AMP Adenylate kinase Rx ATP + AMP ↔ ADP + ADP Maintains [ATP] Build up of AMP limits this Rx Convert AMP IMP or adenosine IMP and Inosine Can be re-converted to AMP or leaves the body as uric acid Mostly seen in type II muscle fibers Allows AK Rx to occur, maintaining high ATP concentrations 5-nucleotidase
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Purine nucleotide cycle
Occurs in cytoplasm AMP deaminase AMP to IMP Ammonia formation Activated by decrease in energy charge Adenylosuccinate synthetase IMP to adenylosuccinate Loss of Pi Adenylosuccinate lyase Adenylosuccinate to AMP Fumarate produced Purpose of cycle Maintenance of cellular energy charge Recycling of adenylate pool
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Reamination in the PNC Adenylosuccinate synthetase and lyase
Reamination occurs in recovery Fumarate is produced Helps maintain the Kreb’s cycle (6th step) Ammonia is produced Excreted in urine Deamination: Helps maintain energy charge during contractions Reamination: Replenished muscle adenylate pool
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