title: Sulphydryl groups in photosynthetic energy conservation. I. Light-dependent inhibition of photophosphorylation by the sulphydryl reagent 2-2'dithio bis-(5-nitropyridine).
abstract: 1. The sulphydryl reagent 2-2'dithio bis-(5-nitropyridine) (DTNP) inhibited photophosphorylation when the chloroplasts were preincubated with the reagent in the light. A maximum inhibition of about 50% was obtained in the presence of pyocyanine and MgCl 2 at 0.3 mumol DTNP per mg chlorophyll and was completed in about 40 s of preillumination. 2. Dithioerythritol, ADP plus Pi (or arsenate) and uncouplers prevented the inhibition when present during the preillumination while phloridzin, Dio-9 and discarine B were ineffective. Low concentrations of ADP or ATP afforded partial protection but other nucleotides had no effect. 3. DTNP inhibited the coupled electron transport rate to the basal level and had no effect on the uncoupled electron transport. The stimulation of proton uptake and inhibition of electron transport by ATP was prevented by DTNP. 4. The trypsin-activated but not the light- and dithioerythritol-triggered ATPase was inhibited by light preincubation of chloroplasts with DTNP. 5. Reversal of DTNP inhibition of photophosphorylation was obtained by a second preillumination in the presence of thiol groups. 6. More DTNP reacted with chloroplasts in the light than in the dark. Two mol of thione were formed in the light per mol of DTNP disappeared. 7. The results suggested that DTNP inhibition is related to the oxidation by DTNP of chloroplast vicinal dithiols probably exposed by a light-induced conformational change.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D002736:Chloroplasts / Q000187:drug effects / Q000528:radiation effects; D003623:Dark Adaptation; D004220:Disulfides / Q000494:pharmacology; D004579:Electron Transport / Q000187:drug effects / Q000528:radiation effects; D008027:Light; D010785:Photophosphorylation / Q000187:drug effects* / Q000528:radiation effects; D010788:Photosynthesis / Q000187:drug effects; D011725:Pyridines / Q000494:pharmacology*; D011830:Radiation Effects; D013439:Sulfhydryl Reagents / Q000494:pharmacology*; D014357:Trypsin / Q000494:pharmacology; D014475:Uncoupling Agents / Q000494:pharmacology
chemical_list: D004220:Disulfides; D011725:Pyridines; D013439:Sulfhydryl Reagents; D014475:Uncoupling Agents; D000255:Adenosine Triphosphate; D014357:Trypsin