The cytochrome b 6 f (Cyt b 6 f) complex, which functions as a plastoquinol-plastocyanin oxidoreductase and mediates the linear electron flow between photosystem II (PSII) and photosystem I (PSI) and the cyclic electron flow around PSI, was isolated from spinach (Spinacia oleracea L.) chloroplasts using n-octyl-β-D-glucopyranoside (β-OG). The preparation was also able to catalyze the peroxidase-like reaction in the presence of hydrogen peroxide (H 2 O 2 ) and guaiacol. The optimal conditions for peroxidase activity of the preparation included: pH 3.6, ionic strength 0.1, and temperature 35ºC. The apparent Michaelis constant (K m ) values for H 2 O 2 and guaiacol were 50 mM and 2 mM, respectively. The bimolecular rate constant (k obs ) was about 26 M -1 s -1 and the turnover number (K cat ) was about 60 min -1 (20 mM guaiacol, 100 mM sodium phosphate, pH 3.6, 25°C, [H 2 O 2 ]<100mM). These parameters were similar to those of several other heme-containing proteins, such as myoglobin and Cyt c.Additional key words: cytochrome b 6 f complex; guaiacol; heme-containing protein; hydrogen peroxide; peroxidase activity.

No abstract