A laser flash absorption spectroscopy study of Anabaena sp. PCC 7119 flavodoxin photoreduction by photosystem I particles from spinach

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Abstract
Electron transfer from P700 in photosystem I (PSI) particles from spinach to Anabaena sp. PCC 7119 flavodoxin has been studied using laser flash absorption spectroscopy. A non-linear protein concentration dependence of the rate constants was obtained, suggesting a two-step mechanism involving complex formation (k=3.6 × 107 M−1· s−1) followed by intracomplex electron transfer (k=270 s−1). The observed rate constants had a biphasic dependence on the concentrations of NaCl or MgCl2 with maximum values in the 40–80 mM range for NaCl and 4–12 mM for MgCl2. To our knowledge, this is the first time that the kinetics of PSI-dependent flavodoxin photoreduction have been determined.