The peroxidase activity of cytochrome b 6 f complex from spinach chloroplasts

Author: Chen X.   Hou C.   Li L.   Kuang T.  

Publisher: Springer Publishing Company

ISSN: 0300-3604

Source: Photosynthetica, Vol.48, Iss.1, 2010-03, pp. : 3-8

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Abstract

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.