BCHOBI 812

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BCH/OBI 812 September 19, 2002 C. Waechter
MEMBRANE CHANNELS AND PUMPS Stryer-Chapter 13
Sodium Pump a Na/K-ATPase Structure
Heterotetramer a 112 kDa-8 TMDs b 35 kDa
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Molecular mechanism for Na/K transport The
formation of a b-aspartyl phosphoryl intermediate
causes a conformational change in the pump
everting the Na- binding site to face the
outside of the cell.
(P-type ATPase)
Digitalis inhibits pump by blocking K-activated
dephosphorylation
Loss of sodium gradient increases intracellular
calcium ions which increases force of
contraction Used to treat congestive heart
failure
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The sarcoplasmic reticulum (SR) Ca-ATPase pumps
calcium ions into the SR by a mechanism similar
to the sodium pump.----a single 110 kDa
polypeptide Another P-type ATPase
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(No Transcript)
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Active versus passive transport Calculation
of free energy change(Stryer-p. 347)
C1
C2
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
G
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The electrochemical gradient created by the
sodium pump can be used for the active
transport of glucose via the Na/glucose symporter
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Antiporters and symporters are two basic types of
secondary transport sytems
The sodium/calcium exchanger in the plasma
membrane of animal cells is an example of an
antiporter
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Lactose permease in E. coli is an example of a
symporter utilizing the free energy of the proton
gradient across the cytoplasmic membrane
(symporter)
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Acetylcholine Receptor structure and function as
a channel (Stryer-p. 355)
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(Heteropentamer)
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Sodium Channel A voltage-gated channel with 24
transmembrane helices that was first isolated as
a tetrodotoxin receptor. Structure has four
repeating units (I-IV) S1, S2, S3, S5 and S6 are
hydrophobic segments and S4 is highly positive
with many Arg and Lys residues which serves as
the voltage sensor.
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Potassium channels are homologous to sodium
channels Two site model for rapid rates in
potassium channel K ejected by electrostatic
repulsion--------