Abstract
In maize chloroplasts, the ratio of HCO3− (anion) binding sites to high-affinity atrazine binding sites is unity. In the dark, atrazine noncompetitively inhibits the binding of half of the HCO3− to the photosystem II (PSII) complexes. The inhibition of binding saturates at 5 micromolar atrazine, little inhibition is seen at 0.5 micromolar atrazine, although the high-affinity herbicide binding sites are nearly filled at this concentration. This means that HCO3− and atrazine interact noncompetitively at a specific low-affinity herbicide binding site that exists on a portion of the PSII complexes. Light abolishes the inhibitory effects of atrazine on HCO3− binding. Based on the assumption that there is one high-affinity atrazine binding site per PSII complex, we conclude that there is also only one binding site for HCO3− with a dissociation constant near 80 micromolar. The location of the HCO3− binding site, and the low-affinity atrazine binding site, is not known.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Diner B. Cooperativity between photosystem II centers at the level of primary electron transfer. Biochim Biophys Acta. 1974 Dec 19;368(3):371–385. doi: 10.1016/0005-2728(74)90182-0. [DOI] [PubMed] [Google Scholar]
- Gardner G. Azidoatrazine: photoaffinity label for the site of triazine herbicide action in chloroplasts. Science. 1981 Feb 27;211(4485):937–940. doi: 10.1126/science.211.4485.937. [DOI] [PubMed] [Google Scholar]
- Jursinic P., Stemler A. Changes in [C]Atrazine Binding Associated with the Oxidation-Reduction State of the Secondary Quinone Acceptor of Photosystem II. Plant Physiol. 1983 Nov;73(3):703–708. doi: 10.1104/pp.73.3.703. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Pfister K., Radosevich S. R., Arntzen C. J. Modification of Herbicide Binding to Photosystem II in Two Biotypes of Senecio vulgaris L. Plant Physiol. 1979 Dec;64(6):995–999. doi: 10.1104/pp.64.6.995. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Stemler A. Forms of Dissolved Carbon Dioxide Required for Photosystem II Activity in Chloroplast Membranes. Plant Physiol. 1980 Jun;65(6):1160–1165. doi: 10.1104/pp.65.6.1160. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Stemler A., Jursinic P. The effects of carbonic anhydrase inhibitors formate, bicarbonate, acetazolamide, and imidazole on photosystem II in maize chloroplasts. Arch Biochem Biophys. 1983 Feb 15;221(1):227–237. doi: 10.1016/0003-9861(83)90139-x. [DOI] [PubMed] [Google Scholar]
- Tischer W., Strotmann H. Relationship between inhibitor binding by chloroplasts and inhibition of photosynthetic electron transport. Biochim Biophys Acta. 1977 Apr 11;460(1):113–125. doi: 10.1016/0005-2728(77)90157-8. [DOI] [PubMed] [Google Scholar]