Spectral and kinetic characterization of electron acceptor A1 in a Photosystem I core devoid of iron-sulfur centers FX, FB and FA

Klaus Brettel, John H. Golbeck

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Abstract

The kinetic and spectroscopic properties of the secondary electron acceptor A1 were determined by flash absorption spectroscopy at room and cryogenic temperatures in a Photosystem I (PS I) core devoid of the iron-sulfur clusters FX, FB and FA. It was shown earlier (Warren, P.V., Golbeck, J.H. and Warden, J.T. (1993) Biochemistry 32: 849-857) that the majority of the flash-induced absorbance increase at 820 nm, reflecting formation of P700+, decays with a t1/2 of 10 μs due to charge recombination between P700+ and A1-. Following A1- directly around 380 nm, where absorbance changes due to the formation of P700+ are negligible, two major decay components were resolved in this study with t1/2 of ≈ 10 μs and 110 μs at an amplitude ratio of ≈ 2.5:1. The difference spectra between 340 and 490 nm of the two kinetic phases are highly similar, showing absorbance increases from 340 to 400 nm characteristic of the one-electron reduction of the phylloquinone A1. When measured at 10 K, the flash-induced absorbance changes around 380 nm can be fitted with two decay phases of t1/2 ≈ 15 μs and 150 μs at an amplitude ratio ≈ 1:1. The difference spectra of both kinetic phases from 340 to 400 nm are similar to those determined at 298 K and are therefore attributed to charge recombination in the pair P700+A1-. These results indicate that the backreaction between P700+ and A1- is multiphasic when FX, FB and FA are removed, and only slightly temperature dependent in the range of 298 K to 10 K.

Original languageEnglish (US)
Pages (from-to)183-193
Number of pages11
JournalPhotosynthesis research
Volume45
Issue number3
DOIs
StatePublished - Sep 1 1995

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Plant Science
  • Cell Biology

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