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The drug ornidazole inhibits photosynthesis in a different mechanism described for protozoa and anaerobic bacteria.

Authors
  • Marcus, Yehouda1
  • Tal, Noam2
  • Ronen, Mordechai1
  • Carmieli, Raanan3
  • Gurevitz, Michael1
  • 1 Department of Plant Molecular Biology & Ecology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 6997801, Israel. , (Israel)
  • 2 Department of Chemistry, Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel. , (Israel)
  • 3 The EPR Laboratory, Chemical Research Support, Faculty of Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel. , (Israel)
Type
Published Article
Journal
Biochemical Journal
Publisher
Portland Press
Publication Date
Dec 01, 2016
Volume
473
Issue
23
Pages
4413–4426
Identifiers
PMID: 27647935
Source
Medline
Keywords
License
Unknown

Abstract

Ornidazole of the 5-nitroimidazole drug family is used to treat protozoan and anaerobic bacterial infections via a mechanism that involves preactivation by reduction of the nitro group, and production of toxic derivatives and radicals. Metronidazole, another drug family member, has been suggested to affect photosynthesis by draining electrons from the electron carrier ferredoxin, thus inhibiting NADP+ reduction and stimulating radical and peroxide production. Here we show, however, that ornidazole inhibits photosynthesis via a different mechanism. While having a minute effect on the photosynthetic electron transport and oxygen photoreduction, ornidazole hinders the activity of two Calvin cycle enzymes, triose-phosphate isomerase (TPI) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Modeling of ornidazole's interaction with ferredoxin of the protozoan Trichomonas suggests efficient electron tunneling from the iron-sulfur cluster to the nitro group of the drug. A similar docking site of ornidazole at the plant-type ferredoxin does not exist, and the best simulated alternative does not support such efficient tunneling. Notably, TPI was inhibited by ornidazole in the dark or when electron transport was blocked by dichloromethyl diphenylurea, indicating that this inhibition was unrelated to the electron transport machinery. Although TPI and GAPDH isoenzymes are involved in glycolysis and gluconeogenesis, ornidazole's effect on respiration of photoautotrophs is moderate, thus raising its value as an efficient inhibitor of photosynthesis. The scarcity of Calvin cycle inhibitors capable of penetrating cell membranes emphasizes on the value of ornidazole for studying the regulation of this cycle.

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