The peroxidase activity of cytochrome b ₆ f complex from spinach chloroplasts
2010
Chen, X. B | Hou, C | Li, L. B | Kuang, T. Y
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 (H₂O₂) and guaiacol. The optimal conditions for peroxidase activity of the preparation included: pH 3.6, ionic strength 0.1, and temperature 35°C. The apparent Michaelis constant (K m) values for H₂O₂ 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, [H₂O₂]<100mM). These parameters were similar to those of several other heme-containing proteins, such as myoglobin and Cyt c.
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