This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Web of Science (79) Citing Articles via Google Scholar Google Scholar Articles by Ort, D. R. Articles by Izawa, S. Search for Related Content PubMed PubMed Citation Articles by Ort, D. R. Articles by Izawa, S. Agricola Articles by Ort, D. R. Articles by Izawa, S.

Articles

Studies on the Energy-coupling Sites of Photophosphorylation

II. Treatment of Chloroplasts with NH₂OH Plus Ethylenediaminetetraacetate to Inhibit Water Oxidation while Maintaining Energy-coupling Efficiencies ¹

^a Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan 48824

Artificial electron donors to photosystem II provide an important means for characterizing the newly discovered site of energy coupling near photosystem II. However, water oxidation must be completely abolished, without harming the phosphorylation mechanism, for these donor reactions and the associated phosphorylation to withstand rigorous quantitative analysis. In this paper we have demonstrated that treatment of chloroplasts with hydroxylamine plus EDTA at pH 7.5 in the presence of Mg²⁺ followed by washing to remove the amine is a highly reliable technique for this purpose. The decline of the Hill reaction and the coupled phosphorylation during the treatment were carefully followed. No change in the efficiency of phosphorylation (P/e₂ 1.0-1.1) was observed until the reactions became immeasurable. Photosystem I-dependent reactions, such as the transfer of electrons from diaminodurene or reduced 2,6-dichlorophenolindophenol to methylviologen, and the associated phosphorylation were totally unaffected. It is clear that the hydroxylamine treatment is highly specific, with no adverse effect on the mechanism of phosphorylation itself. Benzidine photooxidation via both photosystems II and I in hydroxylamine-treated chloroplasts (electron acceptor, methylviologen; assayed as O₂ uptake) supports phosphorylation with the same efficiency as that observed for the normal Hill reaction (P/e₂ = 1.1). An apparent P/e₂ ratio of 0.6 was computed for the photooxidation of ascorbate.

This article has been cited by other articles:

				R. G. Ewy and R. A. Dilley Distinguishing between Luminal and Localized Proton Buffering Pools in Thylakoid Membranes Plant Physiology, February 1, 2000; 122(2): 583 - 596. [Abstract] [Full Text]