Induction of the H+ Release from Thylakoid Membranes by Illumination in the Presence of Protonophores at High Concentrations |
| |
Authors: | Yamasaki, Hideo Furuya, Shigeki Kawamura, Akira Ito, Akio Okayama, Shigeki Nishimura, Mitsuo |
| |
Affiliation: | 1Department of Biology, Faculty of Science, Kyushu University Higashi-ku, Fukuoka, 812 Japan 2Department of Molecular Biology, Graduate School of Medical Science, Kyushu University Higashi-ku, Fukuoka, 812 Japan 3Department of Chemistry, Faculty of Science, Kyushu University Higashi-ku, Fukuoka, 812 Japan 4Biological Laboratory, College of General Education, Kyushu University Ropponmatsu, Fukuoka, 810 Japan |
| |
Abstract: | The generally observed light-induced uptake of protons intothe thylakoid lumen is diminished by adding protonophores. Insteadof the H+ uptake, the release of protons was observed duringillumination in the presence of various protonophores at highconcentrations, namely, 1 µM nigericin, 10 µM carbonylcyanidem-chlorophenylhydrazone or 30 µM gramicidin. An uncoupler,NH4C1 (4 mM), and a detergent, Triton X-100 (0.02%), also inducedthe H+ release but a K+ ionophore, valinomycin, did not. Theamount of H+ released reached about 100 nmol H+ (mg Chl)1at pH 7.5 under continuous illumination. The rate of the H+release was similar to that of the conventional H+ uptake butits dark relaxation was much slower than that of the H+ uptake.We compared the H+ release in protonophore-added thylakoidswith the previously reported H+ release in coupling factor 1(CF1-depleted thylakoids. The H+ release in thylakoids withnigericin showed similar characteristics to that in CF1-depletedthylakoids in terms of their responses to pH, phenazine methosulfateand light intensity. Both types of H+ release were relativelyinsensitive to DCMU and were stimulated somewhat by DCMU atlow concentrations (around 200 nM). Nigericin did not inhibitthe superoxide dismutase activity of the membranes. These resultsindicate that the H+ release in protonophore-added thylakoidsand that in CF1 depleted thylakoids involve the same mechanismand that water-derived protons from PS II that result from animpairment of the activity of superoxide dismutase, as previouslyproposed, are not involved. Judging from the rate of electronflow and the lumenal acidification under the illumination, weconclude that the H+ release is a light-dependent scalar processwhich can be observed in thylakoid membranes with high H+ permeability.The H+ release of this type was not observed in mitochondriafrom rat liver or in chromatophores from Rhodobacter sphaeroides. (Received November 29, 1990; Accepted June 27, 1991) |
| |
Keywords: | |
本文献已被 Oxford 等数据库收录! |
|