NA/K ATPASE

[LOLAHA]

Lipid vesicles (small spherical bilayers) provide an ideal in vitro system for the study of
pumps and channels. You have prepared lipid vesicles that contain Na+/K+ pumps. The pumps are
oriented such that the portion of the pump that normally faces the cytoplasm is facing the outside of the
vesicle. Predict what would happen under each of the following conditions (for simplicity, assume that
the ions are pumped in a 1:1 ratio).
A) The solution on the inside and outside of the vesicles contains both ions, but no ATP.
B) The solution inside the vesicle contains both ions; the solution outside contains both ions and
ATP.
C) The solution inside contains sodium ions; the solution outside contains sodium ions plus ATP.
D) The solution as in part B, but the pumps are randomly oriented, some facing outward and some
facing inward.

[LOLAHA]

a) i know that there will be diffusion of ions across the membrane because of the concentration gradient and other channels in the membrane. But the active pump will not work cos there is no ATP.
b) Is this the reverse reaction? K will bind to the active site because of the affinity in the exoplasmic side and the membrane will release it into the cell upon dephosphorylation of the active site, which will cause a conformational change and allow the na to bind to the active site.?????????
c) The sodium ions will be stuck in the active site because k is absent???
d) there will be a normal function and reversed function explained in b???

[JackBean]

a) if there was ion gradient across the membrane, they would be pointless so, no move in a)
b) this should work, but you will see no change except ATP depletion
c) Na+ will be released, but ATPase will be stucked
d) only these, which are oriented in the normal way will work (ATP is only outside)

[LOLAHA]

Jeackbean, thanks for your response. But could you tell me the reasioning behind your ans? Thanks.

[JackBean]

I guess, you know, how it works
http://en.wikipedia.org/wiki/Na%2B/K%2B ... #Mechanism
ATP is required on the intracellular site, that is outside here.

I wrote wrong B, you should see increased Na inside nad K+ ouside

A) you don't have ATP, pump doesn't work at all
B) you have complete mix like in the cell, so it will all work
C) you don't have potassium, so the pump will be locked opened with bound phosphate
D) as I told you, you have ATP only outside, so only these pumps will work