In my cell bio lab we do an experiment to test two compounds for their
effects on light-dependent electron transport in chloroplasts. One is
(diuron), an inhibitor of photosynthetic electron transport. The other
ammonia, an uncoupler. The students are supposed to figure out which is
which from their data.
There is no question that ammonia is an uncoupler, at least for the
students. However, my question is, how does it work? I teach the
that uncouplers collapse the proton gradient by moving protons across
membrane. DNP can move across the membrane both in the protonated and
unprotonated (negative charged) form. However, while ammonia should
membranes fairly easily, ammonium should not, being +charged. The
haven't called me on it yet, but I'd like to know the answer. So far I
haven't found anything in books.
Can ammonium cross membranes? (From what I know of patch-clamping, no).
Does ammonia simply enter the thylakoids and soak up the protons, thus
removing them from the gradient?
Do thylakoids leak ammonium? (I understand they leak Mg2+ and Cl-, so
there's no membrane voltage across them.)
Dr. Gary Coté
Department of Biology
Radford, VA 24142-6931
email: gcote at radford.eduhttp://www.radford.edu:8800/~gcote/