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hulajnoga
Dołączył: 16 Lut 2011
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 Wysłany: Pon 6:49, 14 Mar 2011 Temat postu: sodium pumps |
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structure and function
the na+-k+-atpase is composed of two subunits. the alpha subunit (~113 kd) is the action hero of the pair - it binds atp and both sodium and potassium ions, and contains the phosphorylation site. the smaller beta subunit (~35 kda glycoprotein) is absolutely necessary for activity of the complex. it appears to be critical in facilitating the plasma membrane localization and activation of the alpha subunit.
several isoforms of both alpha and beta subunits have been identified, but aside from kinetic characterizations and tissue distribution, little is known regarding their differential physiologic importance.
uncertainties remain in describing the structure of this molecule, but based on primary amino acid sequence,[link widoczny dla zalogowanych], it is thought to possess 8 or 10 transmembrane domains. considerable information is available to define the amino acids involved in atp and cation binding.
cation transport occurs in a cycle of conformational changes apparently triggered by phosphorylation of the [link widoczny dla zalogowanych]. as currently understood,[link widoczny dla zalogowanych],[link widoczny dla zalogowanych],[link widoczny dla zalogowanych], the sequence of events can be summarized as follows:
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