Forti Giorgio
Dipartimento di Biologia dell'Università e Istituto di Biofisica del CNR - Via Celoria 26, Milano 20133, Italy.
Biochim Biophys Acta. 2008 Nov;1777(11):1449-54. doi: 10.1016/j.bbabio.2008.08.011. Epub 2008 Sep 10.
It is reported that O(2) is required for the activation of photosynthesis in dark adapted Chlamydomonas reinhardtii in State 1, under low light intensity. The concentration of dissolved O(2) of ca. 9 microM is sufficient to saturate the requirement. When the concentration of O(2) is 3 muM or below, the activation of photosynthesis is strongly inhibited by myxothiazol, a specific inhibitor of the mitochondrial cytochrome bc(1). The effect of this inhibitor decreases as the O(2) concentration is raised, to disappear completely above 50 muM. Low concentrations of uncouplers delay the activation of photosynthesis, but do not inhibit it when steady state is reached. It is concluded that in State 1 C. reinhardtii mitochondrial respiration is required for the activation of photosynthesis upon illumination of dark adapted cells only when the concentration of O(2) is too low (less than 5 muM) to allow an appreciable activity of the Mehler reaction. The role of respiration does not seem to be due to the synthesis of ATP by oxidative phosphorylation, because photosynthesis activation is not sensitive to oligomycin.
据报道，在低光照强度下，黑暗适应的莱茵衣藻处于状态1时，光合作用的激活需要O₂。约9微摩尔的溶解O₂浓度足以满足需求。当O₂浓度为3微摩尔或更低时，光合作用的激活受到粘噻唑（线粒体细胞色素bc₁的特异性抑制剂）的强烈抑制。随着O₂浓度升高，这种抑制剂的作用减弱，在50微摩尔以上时完全消失。低浓度的解偶联剂会延迟光合作用的激活，但在达到稳态时不会抑制它。得出的结论是，在状态1下，只有当O₂浓度过低（低于5微摩尔）以至于无法使梅勒反应有明显活性时，黑暗适应细胞光照后光合作用的激活才需要莱茵衣藻线粒体呼吸。呼吸的作用似乎不是由于氧化磷酸化合成ATP，因为光合作用的激活对寡霉素不敏感。
