Question

explain why the rate of transport of potassium ions across a bilayer of dimyristoyl phosphatidyl choline by valinomycin greatly decrease when the temperatue is gradually reduced from 25 to 15 C whereas the rate of transport of potassium ions by gramicidin D is almost unchanged under similar circumstances?

Answer 1

In case of valinomycin,he transport of potassium ions across a bilayer of dimyristoyl phosphatidyl choline depends on the state of the membrane.At lower temperature,a phase transition occurs in the bilayer and freezing occurs that changes bilayer to a solid phase.As the membrane freezes, valiomycin is not able to able to diffuse across the bilayer.For valinomycin to work, it has to diffuse across the membrane ,make complexes with potassium ions so that the entire complex can dissolve in the lipid membrane.In case of gramicidin D, this is almost underchanged under similar conditions because it is not effected by phase change of the bilayer or when bilayer is frozen.Gramicidin possesess continuous channels within its molecules that extend across the membrane forming a route for transmembrane movement even when the bilayer is frozen.