Deconvolution Analysis of Photoacoustic Waves of Electron Transfer in Photosystem I of menG Null Mutant of Synechocystis sp. PCC 6803
Inactivating the menG gene causes 2-phytyl-1,4-naphthoquinone (Q) to be presented as a quinone acceptor in PSI of Synechocystis sp. PCC 6803. The electron transfer from Q− to FX is slowed to 600 ns in the menG null mutant [Sakuragi Y, B Zybailov G Shen, AD Jones, PR Chitnis, A van der Est, R Bittl, S Zech, D Stehlik, JH Golbeck, and DA Bryant. (2002) Biochemistry 41: 394–405]. Despite of the alternation of kinetics, the thermodynamics of electron transfer in the mutant is not known. In this work, we conducted deconvolution analysis on photoacoustic waves of the menG null mutants and the wild type strains of Synechocystis sp. PCC 6803 obtained by pulsed photoacoustics on the microsceond time scale. The fit by convolution of menG photoacoustic waves revealed a large volume contraction (−28 ± 2 Å3) for the P700* → Q step and a positive volume change (+5 ± 2 Å3) for the Q− → FA/B step. The enthalpy changes were −0.7 ± 0.2 eV for the P700* → Q step and +0.5 ± 0.2 eV for the Q− → FA/B step, respectively. Taking the free energy of −0.7 eV and −0.1 eV for these steps, the data presented here shows that the Q− to FA/B electron transfer step in the menG null mutant is entropy driven.
KeywordsEnthalpy Entropy Volume change Photoacoustics Electron transfer Photosystem I menG
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