(Solved): Q1. (1.5 points each) Monensin is a sodium/proton ionophore. Figure 1 summarizes the observation tha ...

Q1. (1.5 points each) Monensin is a sodium/proton ionophore. Figure 1 summarizes the

observation that the neutral complexes of monensin with either a proton or a sodium ion can

cross the membrane, while the uncomplexed, negatively charged form cannot.

Figure 1: Minesin permeates the membrane when complexed with sodium or proton ions

Show that for the full reaction cycle:

a) If pH = 7 is ?xed by bu?ers on both the inside and outside of the membrane vesicles, and

if the initial concentrations of sodium are [Na+]out = 20 mM, and [Na+]in = 1 mM, which

direction is the net reaction favorable for?

b) Does this reaction a?ect on membrane potential? Why?

\( M^{-}\left(H^{+}\right)_{\text {out }} \underset{H_{\text {out }}^{+}}{\longrightarrow} M_{\text {out }}^{-} \stackrel{N_{\text {out }}^{+}}{\longrightarrow} M^{-}\left(\mathrm{Na}^{+}\right)_{\text {out }} \) \( M^{-}\left(H^{+}\right)_{\text {in }} \underset{H_{\text {in }}^{+}}{\longrightarrow} M_{\text {in }}^{-} \stackrel{N a_{\text {in }}^{+}}{\longrightarrow} M^{-}\left(\mathrm{Na}^{+}\right)_{\text {in }} \)