ATP

Examples of ATP in the following topics:

• F10 ATP Synthase

  • ATP synthase is an important enzyme that provides energy for the cell to use through the synthesis of adenosine triphosphate (ATP).
  • ATP is the most commonly used "energy currency" of cells from most organisms.
  • The overall reaction sequence is: ATP synthase + ADP + Pi → ATP Synthase + ATP
  • Oligomycin, an antibiotic, is able to inhibit the FO unit of ATP synthase.
  • E. coli ATP synthase is the simplest known form of ATP synthase, with 8 different subunit types.

• Respiration and Proton Motive Force

  • Aerobic reactions require oxygen for ATP generation.
  • Glucose + 2 NAD+ + 2 Pi + 2 ADP → 2 pyruvate + 2 NADH + 2 ATP + 2 H+ + 2 H2O + heat
  • They are able to do this with the help of the solar-driven enzyme bacteriorhodopsin, which is used to drive the molecular motor enzyme ATP synthase to make the necessary conformational changes required to synthesize ATP.
  • The F1FO ATP synthase is a reversible enzyme.
  • Large enough quantities of ATP cause it to create a transmembrane proton gradient.

• The Reverse TCA Cycle

  • Reverse TCA, a form of carbon fixation, utilizes numerous ATP molecules, hydrogen and carbon dioxide to generate an acetyl CoA.
  • ATP citrate lyase is one of the key enzymes that function in reverse TCA.
  • ATP citrate lyase is the enzyme responsible for cleaving citrate into oxaloacetate and acetyl CoA.
  • 4) succinate is converted to succinyl-CoA (ATP is hydrolyzed to ADP+Pi)
  • 8) ATP citrate lyase is then used to convert citrate to oxaloacetate and acetyl CoA (ATP is hydrolyzed to ADP and Pi).

• The Entner–Doudoroff Pathway

  • The free energy released in this process is used to form the high-energy compounds ATP (adenosine triphosphate) and NADH (reduced nicotinamide adenine dinucleotide).
  • The Entner–Doudoroff pathway also has a net yield of 1 ATP for every glucose molecule processed, as well as 1 NADH and 1 NADPH.
  • By comparison, glycolysis has a net yield of 2 ATP and 2 NADH for every one glucose molecule processed.
  • Most organisms that use the pathway are aerobes due to the low ATP yield per glucose such as Pseudomonas, a genus of Gram-negative bacteria, and Azotobacter, a genus of Gram-negative bacteria.

• Proton Reduction

  • This potential energy is used for the synthesis of ATP by phosphorylation.
  • In respiring bacteria under physiological conditions, ATP synthase, in general, runs in the opposite direction, creating ATP while using the proton motive force created by the electron transport chain as a source of energy.
  • The same process takes place in the mitochondria, where ATP synthase is located in the inner mitochondrial membrane, so that F1 part sticks into the mitochondrial matrix where ATP synthesis takes place.
  • The resulting current drives ATP synthesis from ADP and inorganic phosphate.
  • Instead, it only uses substrate-level phosphorylation to produce ATP.

• Nitrogen Fixation Mechanism

  • Substrate binding and reduction takes place on component I, which binds to ATP and ferredoxin or flavodoxin proteins (Fdx or Fld) (see step B).
  • The hydrolysis of ATP supplies the energy for the reaction while the Fdx/Fld proteins supply the electrons.
  • ATP is not hydrolyzed to ADP until component II transfers an electron to component I (see step C and D). 21-25 ATPs are required for each N2 fixed.
  • B) ATP binds to component II, which receives electrons from an electron donor (ferredoxin or flavodoxin); binding of ATP induces an allosteric conformational change which allows association of the two proteins.
  • C) Electrons are further shuttled to the iron-molybdenum cofactor (FeMoco), and ATP is hydrolised to ADP.

• Cofactors and Energy Transitions

  • As an example, the total quantity of ATP in the human body is about 0.1 mole.
  • This ATP is constantly being broken down into ADP, and then converted back into ATP.
  • Therefore, at any given time, the total amount of ATP + ADP remains fairly constant.
  • In typical situations, humans use up their body weight of ATP over the course of the day.
  • This means that each ATP molecule is recycled 1,000 to 1,500 times daily.

• ABC Transporters

  • ABC transporters are a protein superfamily that all have an ATP binding cassette and transport substances across membranes.
  • ATP-binding cassette transporters (ABC-transporters) are members of a protein superfamily that is one of the largest and most ancient families with representatives in all extant phyla from prokaryotes to humans.
  • ABC transporters are transmembrane proteins that utilize the energy of adenosine triphosphate (ATP) hydrolysis to carry out certain biological processes including translocation of various substrates across membranes and non-transport-related processes such as translation of RNA and DNA repair.
  • Proteins are classified as ABC transporters based on the sequence and organization of their ATP-binding cassette (ABC) domain(s).

• Intermediates Produced During the Calvin Cycle

  • This process requires the enzyme RuBisCO and both ATP and NADPH.
  • During phase 2 of this cycle, the newly formed 3-PGA undergoes phosphorylation by the enzyme phosphoglycerate kinase which utilizes ATP.
  • The ADP product that is produced via the breakdown of ATP will be utilized in additional pathways and be converted back into ATP.
  • The inter conversions of ATP to ADP and ADP to ATP is a key process in supplying energy in numerous processes.
  • The phosphate ions are used in processes such as buffering cells, conversions of AMP/ADP to ATP and production of materials involved in structure such as bone and teeth.

• Sodium Pumps as an Alternative to Proton Pumps

  • It is now known that the carrier is an ATP-ase and that it pumps three sodium ions out of the cell for every two potassium ions pumped in.
  • The pump, while binding ATP, binds 3 intracellular Na+ ions.
  • ATP is hydrolyzed, leading to phosphorylation of the pump at a highly conserved aspartate residue and subsequent release of ADP .
  • ATP binds, and the process starts again.
  • First, Na+-based membrane energetics could improve the versatility of a pathogen by providing it with additional means of ATP synthesis, motility and solute uptake.