Division of Physics and Astronomy, Department of Biophysics, VU University, Amsterdam, The Netherlands.
J Phys Chem B. 2013 Aug 8;117(31):9121-8. doi: 10.1021/jp307420p. Epub 2013 Jul 29.
The orange carotenoid protein (OCP) is a crucial player in the process of nonphotochemical quenching in a large number of cyanobacteria. This water-soluble protein binds one pigment only, the keto carotenoid 3'-hydroxyechinenone, and needs to be photoactivated by strong (blue-green) light in order to induce energy dissipation within or from the phycobilisome, the main light harvesting system of these organisms. We performed transient-absorption spectroscopy on OCP samples frozen in the inactive and active forms at 77 K. By making use of target analysis we determined the excited state properties of the active form. Our results show that OCP photoactivation modifies the carotenoid excited state energy landscape. More specifically the photoactivated OCP is characterized by one state with predominantly ICT character (ICT/S1) and a lifetime of 2.3 ps, and another state with mainly S1 character (S1/ICT) with a lifetime of 7.6 ps. We also show that the kinetic model is fully consistent with the RT data obtained earlier (Berera et al., J. Phys. Chem. B 2012, 116, 2568-2574). We propose that this ICT/S1 state acts as the quencher in the OCP mediated nonphotochemical quenching.
橙黄色类胡萝卜素蛋白（OCP）在许多蓝藻的非光化学猝灭过程中是一个关键的参与者。这种水溶性蛋白只结合一种色素，即酮类类胡萝卜素 3'-羟基虾青素，并需要通过强（蓝绿色）光进行光激活，以便在藻胆体（这些生物体的主要光收集系统）内或从藻胆体诱导能量耗散。我们在 77 K 下对处于非活性和活性形式的 OCP 样品进行了瞬态吸收光谱研究。通过使用目标分析，我们确定了活性形式的激发态性质。我们的结果表明，OCP 的光激活改变了类胡萝卜素激发态能量景观。更具体地说，光激活的 OCP 的特征是一个具有主要 ICT 特征（ICT/S1）和 2.3 ps 寿命的状态，以及另一个具有主要 S1 特征（S1/ICT）和 7.6 ps 寿命的状态。我们还表明，该动力学模型与先前获得的 RT 数据（Berera 等人，J. Phys. Chem. B 2012，116，2568-2574）完全一致。我们提出，这种 ICT/S1 状态作为 OCP 介导的非光化学猝灭中的猝灭剂。
