Calcium ATPase

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Calcium ATPase is a form of P-ATPase which transfers calcium after a muscle has contracted.

General characteristics of ATPases

ATPases (or ATP synthases) are membrane-bound enzymecomplexes/ion transporters that combine the synthesis and/or hydrolysis of adenosine triphosphate (ATP) with the transport of protons across a plasma membrane. ATPases can harness the energy from an electrochemical proton gradient, using the flux of ions across the membrane via the ATPase proton channel to drive the synthesis of ATP. Some ATPases work in reverse, using the energy from the hydrolysis of ATP to create a proton gradient. There are different types of ATPases, which can differ in function (ATP synthesis and/or hydrolysis), structure (F-, V- and A-ATPases contain rotary motors) and in the type of ions they transport.

  • F-ATPases (F1F0-ATPases) in mitochondria, chloroplasts and bacterial plasma membranes are the prime producers of ATP, using the proton gradient generated by oxidative phosphorylation (mitochondria) or photosynthesis (chloroplasts).
  • V-ATPases (V1V0-ATPases) are primarily found in eukaryotic vacuoles, catalysing ATP hydrolysis to transport solutes and lower pH in organelles.
  • A-ATPases (A1A0-ATPases) are found in Archaea and function like F-ATPases.
  • P-ATPases (E1E2-ATPases) are found in bacteria and in eukaryotic plasma membranes and organelles, and function to transport a variety of different ions across membranes.
  • E-ATPases are cell-surface enzymes that hydrolyse a range of NTPs, including extracellular ATP.

P-ATPases (sometime known as E1-E2 ATPases) are found in bacteria and in a number of eukaryotic plasma membranes and organelles. P-ATPases function to transport a variety of different compounds, including ions and phospholipids, across a membrane using ATP hydrolysis for energy. There are many different classes of P-ATPases, each of which transports a specific type of ion: H+, Na+, K+, Mg2+, Ca2+, Ag+ and Ag2+, Zn2+, Co2+, Pb2+, Ni2+, Cd2+, Cu+ and Cu2+. P-ATPases can be composed of one or two polypeptides, and can usually assume two main conformations called E1 and E2.

Genes

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