Physicochemical Properties of Ferredoxin from Chlamydomonas reinhardii

Ferredoxin from Chlam ydom onas reinhardii has been purified to electrophoretic hom ogeneity by an easy and fast procedure with a high yield (25—30 mg/250 g wet weight of cells). An average molecular weight of 11800 was calculated from sedimentation coefficient (1.70 S) and Stokes radius (1.75 nm) data, sodium dodecyl sulfate-electrophoresis, and amino acid composition. A b­ sorption spectrum showed maxima at 276, 330, 420 and 460 nm in the oxidized form, with an absorption ratio {A A2J A 216) of 0.54 and an extinction coefficient of 8.38 mM_1-c m _1 at 420 nm. Reduced ferredoxin showed a single peak at 276 nm with shoulders at 284, 310, 390, 469 and 537 nm and at liquid helium temperatures gave EPR signals at g = 1.877, 1.951 and 2.045. The protein has an isoelectric point of 3.30, and one (2F e —2S)-cluster per molecule with a midpoint potential, at pH 7.5, o f —410 mV (n = l) . The m olecule of C. reinhardii ferredoxin consists of 95—99 amino acid residues which includes the full com plem ent of amino acids, being alanine the most abundant.