Absorbance difference spectra of the S-state transitions in Photosystem II core particles

✍ Scribed by Peter J. Leeuwen; Claudia Heimann; Hans J. Gorkom

• Book ID: 104622402
• Publisher: Springer
• Year: 1993
• Tongue: English
• Weight: 771 KB
• Volume: 38
• Category: Article
• ISSN: 0166-8595
• DOI: 10.1007/bf00046757

✦ Synopsis

Redox changes of the oxygen evolving complex in PS II core particles were investigated by absorbance difference spectroscopy in the UV-region. The oscillation of the absorbance changes induced by a series of saturating flashes could not be explained by the minimal Kok model (Kok et al. 1970) consisting of a 4-step redox cycle, S O --~ S l --~ S 2 ~ S 3 --* So, although the values of most of the relevant parameters had been determined experimentally. Additional assumptions which allow a consistent fit of all data are a slow equilibration of the S 3 state with an inactive state, perhaps related to Ca2+-release, and a low quantum efficiency for the first turnover after dark-adaptation. Difference spectra of the successive S-state transitions were determined. At wavelengths above 370 rim, they were very different due to the different contribution of a Chl bandshift in each spectrum. At shorter wavelengths, the $1 ~ S z transition showed a difference spectrum similar to that reported by Dekker et al. 1984b and attributed to an Mn(III) to Mn(IV) oxidation.