This work aims to fully elucidate the effects of a trehalose glassy matrix on electron transfer reactions in cyanobacterial Photosystem I (PS I). Forward and backward electron transfer rates from A1A − and A1B − to FX, and charge recombination rates from A0 −, A1B −, A1A −, FX −, and [FA/FB]− to P700 + were measured in P700–FA/FB complexes, P700–FX cores, and P700–A1 cores, both in liquid and in a trehalose glassy matrix at 11% humidity. By comparing CONTIN-resolved kinetic events over 6 orders of time in increasingly simplified versions of PS I at 480 nm, a wavelength that reports primarily A1A −/A1B − oxidation, and over 9 orders of time at 830 nm, a wavelength that reports P700 + reduction and A0 − oxidation, assignments could be made for nearly all of the resolved kinetic phases. Trehalose-embedded PS I samples demonstrated partially arrested forward electron transfer. The fractions of complexes in which electron transfer did not proceed beyond A0, A1 and FX were 53%, 16% and 22%, respectively, with only 10% of electrons reaching the terminal FA/FB clusters. The ~10 μs and ~150 μs components in both liquid and trehalose-embedded PS I were assigned to recombination between A1B − and P700 + and between A1A − and P700 +, respectively. The kinetics and amplitudes of these resolved kinetic phases in liquid and trehalose-embedded PS I samples could be well-fitted by a kinetic model that allowed us to calculate the asymmetrical contribution of the A1A − and A1B − quinones to the electrochromic signal at 480 nm. Possible reasons for these effects are discussed.
All Science Journal Classification (ASJC) codes
- Cell Biology