Lactoperoxidase-catalyzed iodination of chloroplast membranes. II. Evidence for surface localization of Photosystem II reaction centers

C. J. Arntzen, C. Vernotte, J. M. Briantais, P. Armond

Research output: Contribution to journalArticle

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Abstract

The enzyme lactoperoxidase was used to specifically iodinate the surface-exposed proteins of chloroplast lamellae. This treatment had two effects on Photosystem II activity. The first, occurring at low levels of iodination, resulted in a partial loss of the ability to reduce 2,6-dichlorophenolindophenol (DCIP), even in the presence of an electron donor for Photosystem II. There was a parallel loss of Photosystem II mediated variable yield fluorescence which could not be restored by dithionite treatment under anaerobic conditions. The same pattern of inhibition was observed in either glutaraldehyde-fixed or unfixed membranes. Analysis of the lifetime of fluorescence indicated that iodination changes the rate of deactivation of the excited state chlorophyll. We have concluded that iodination results in the introduction of iodine into the Photosystem II reaction center pigment-protein complex and thereby introduces a new quenching. The data indicate that the reaction center II is surface exposed. At higher levels of iodination, an inhibition of the electron transport reactions on the oxidizing side of Photosystem II was observed. That portion of the total rate of photoreduction of DCIP which was inhibited by this action could be restored by addition of an electron donor to Photosystem II. Loss of activity of the oxidizing side enzymes also resulted in a light-induced bleaching of chlorophyll a680 and carotenoid pigments and a dampening of the sequence of O2 evolution observed during flash irradiation of treated chloroplasts. All effects on electron transport on the oxidizing side of Photosystem II could be eliminated by glutaraldehyde fixation of the chloroplast lamellae prior to lactoperoxidase treatment. It is concluded that the electron carriers on the oxidizing side of Photosystem II are not surface localized; the functioning of these components is impaired by structural disorganization of the membrane occurring at high levels of iodination. Our data are in agreement with previously published schemes which suggest that Photosystem II mediated electron transport traverses the membrane.

Original languageEnglish (US)
Pages (from-to)39-53
Number of pages15
JournalBBA - Bioenergetics
Volume368
Issue number1
DOIs
StatePublished - Oct 18 1974
Externally publishedYes

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Lactoperoxidase
Photosystem II Protein Complex
Halogenation
Chloroplasts
Membranes
Electron Transport
2,6-Dichloroindophenol
Glutaral
Electrons
Chlorophyll
Pigments
Fluorescence
Chloroplast Proteins
Dithionite
Enzymes
Carotenoids
Bleaching
Excited states
Iodine
Quenching

ASJC Scopus subject areas

  • Biophysics
  • Medicine(all)

Cite this

Lactoperoxidase-catalyzed iodination of chloroplast membranes. II. Evidence for surface localization of Photosystem II reaction centers. / Arntzen, C. J.; Vernotte, C.; Briantais, J. M.; Armond, P.

In: BBA - Bioenergetics, Vol. 368, No. 1, 18.10.1974, p. 39-53.

Research output: Contribution to journalArticle

Arntzen, C. J. ; Vernotte, C. ; Briantais, J. M. ; Armond, P. / Lactoperoxidase-catalyzed iodination of chloroplast membranes. II. Evidence for surface localization of Photosystem II reaction centers. In: BBA - Bioenergetics. 1974 ; Vol. 368, No. 1. pp. 39-53.
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