Effect of ammonium salts, amines and antibiotics on proton uptake and photophosphorylation in Rhodospirillum rubrum chromatophores

Abstract

1. NH 4Cl inhibits the light-induced proton uptake but not photophosphorylation in chromatophores prepared from Rhodospirillum rubrum. This selective inhibition of proton uptake was also obtained with various amines which are well-known uncouplers in chloroplasts. 2. Addition of ion-transporting antibiotics like valinomycin or nonactin resulted in the inhibition of photophosphorylation with NH 4Cl but not with the other amines. The synergistic inhibition with valinomycin and NH 4Cl was abolished in the presence of K +. 3. Similar results were found also in subchloroplast particles. Both in chromatophores and in subchloroplast particles valinomycin was required to induce the inhibition of photophosphorylation with ammonium nitrate, bicarbonate and acetate as well as chloride. 4. The effect of the ion-transporting antibiotics can be attributed to an enhanced permeability of NH 4 + in their presence. The resulting inhibition of photophosphorylation can be explained by the initiation of an energy-dependent cyclic cation transport involving an active influx of protons coupled with a passive efflux of NH 4 + facilitated by the antibiotics. The results can also be explained according to the chemiosmotic theory, if it is assumed that all the anions tested, namely Cl −, NO 3 −, HCO 3 − and acetate are impermeable in chromatophores as well as in subchloroplast particles.