Regulation of violaxanthin de-epoxidase activity by pH and ascorbate concentration

Charlotte Eva Bratt, Per-Ola Arvidsson, Marie Carlsson, Hans-Erik Åkerlund

Research output: Contribution to journalArticlepeer-review


The activity of violaxanthin de-epoxidase has been studied both in isolated thylakoids and after partial purification, as a function of pH and ascorbate concentration. We demonstrate that violaxanthin de-epoxidase has a Km for ascorbate that is strongly dependent on pH, with values of 10, 2.5, 1.0 and 0.3 mM at pH 6.0, 5.5, 5.0 and 4.5, respectively. These values can be expressed as a single Km±0.1±0.02 mM for the acid form of ascorbate. Release of the protein from the thylakoids by sonication was also found to be strongly pH dependent with a cooperativity of 4 with respect to protons and with an inflexion point at pH 6.7. These results can explain some of the discrepancies reported in the literature and provide a more consistent view of zeaxanthin formation in vivo.
Original languageEnglish
Pages (from-to)169-175
JournalPhotosynthesis Research
Issue number2
Publication statusPublished - 1995

Subject classification (UKÄ)

  • Biological Sciences


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