Passive Entry of CO2 and Its Energy-dependent Intracellular Conversion to HCO3- in Cyanobacteria Are Driven by a Photosystem I-generated ΔμH+

Dan Tchernov, Yael Helman, Nir Keren, Boaz Luz, Itzhak Ohad, Leonora Reinhold, Teruo Ogawa, Aaron Kaplan

Research output: Contribution to journalArticlepeer-review

Abstract

CO2 entry into Synechococcus sp. PCC7942 cells was drastically inhibited by the water channel blocker p-chloromercuriphenylsulfonic acid suggesting that CO2 uptake is, for the most part, passive via aquaporins with subsequent energy-dependent conversion to HCO3 -. Dependence of CO2 uptake on photosynthetic electron transport via photosystem I (PSI) was confirmed by experiments with electron transport inhibitors, electron donors and acceptors, and a mutant lacking PSI activity. CO2 uptake was drastically inhibited by the uncouplers carbonyl cyanide m-chlorophenylhydrazone (CCCP) and ammonia but substantially less so by the inhibitors of ATP formation arsenate and N,N,-dicyclohexylcarbodiimide (DCCD). Thus a ΔμH+ generated by photosynthetic PSI electron transport apparently serves as the direct source of energy for CO2 uptake. Under low light intensity, the rate of CO2 uptake by a high-CO2-requiring mutant of Synechococcus sp. PCC7942, at a CO2 concentration below its threshold for CO2 fixation, was higher than that of the wild type. At saturating light intensity, net CO2 uptake was similar in the wild type and in the mutant IL-3 suggesting common limitation by the rate of conversion of CO2 to HCO3-. These findings are consistent with a model postulating that electron transport-dependent formation of alkaline domains on the thylakoid membrane energizes intracellular conversion of CO2 to HCO3-.

Original languageEnglish
Pages (from-to)23450-23455
Number of pages6
JournalJournal of Biological Chemistry
Volume276
Issue number26
DOIs
StatePublished - 29 Jun 2001
Externally publishedYes

ASJC Scopus subject areas

  • Molecular Biology
  • Biochemistry
  • Cell Biology

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