Ligeza A, Wisniewska A, Subczynski W K, Tikhonov A N
Department of Biophysics, Jagiellonian University, Krakow, Poland.
Biochim Biophys Acta. 1994 Jul 29;1186(3):201-8. doi: 10.1016/0005-2728(94)90179-1.
A new spin-label oximetry approach able to measure the oxygen partial pressure in complex photosynthetic systems has been developed using bovine serum albumin (BSA)-coated light paraffin oil particles containing cholestane spin label (CSL). Paraffin oil particles protect the spin label against the action of chemically active metabolites. The amplitude of the electron paramagnetic resonance (EPR) signal from CSL measured at a saturating microwave power is sensitive to the concentration of oxygen. We demonstrate here the ability of this method to monitor the kinetics of light-induced oxygen production in situ, i.e., in the interior of a bean leaf. The oxygen release, observed during leaf illumination with continuous light, exhibits an overshoot that correlates with the well-known nonmonotonous behaviour of the Photosystem I reaction center, P700. Short-term illumination of isolated bean chloroplasts, suspended in the presence of the electron mediator methylviologen, induces a reversible uptake of oxygen. However, after prolonged illumination, chloroplasts lose their ability to regenerate oxygen in the dark. The exhaustion of oxygen (and oxygen active forms) is accompanied by the loss of CSL paramagnetism and the capacity to photooxidize P700. Comparison of the kinetics of P700 redox transients with oximetric data demonstrates that oxygen concentration is the essential factor controlling electron transport in leaves and isolated chloroplasts.
一种新的自旋标记血氧测定法已经开发出来，该方法能够使用含有胆甾烷自旋标记（CSL）的牛血清白蛋白（BSA）包被的轻质石蜡油颗粒来测量复杂光合系统中的氧分压。石蜡油颗粒可保护自旋标记免受化学活性代谢物的作用。在饱和微波功率下测量的来自CSL的电子顺磁共振（EPR）信号的幅度对氧浓度敏感。我们在此展示了该方法原位监测光诱导产氧动力学的能力，即在蚕豆叶片内部。在用连续光照射叶片期间观察到的氧释放呈现出一个峰值，这与光系统I反应中心P700的众所周知的非单调行为相关。悬浮在电子介质甲基紫精存在下的分离蚕豆叶绿体的短期光照会诱导氧的可逆吸收。然而，长时间光照后，叶绿体在黑暗中失去再生氧的能力。氧（和氧活性形式）的耗尽伴随着CSL顺磁性的丧失以及光氧化P700的能力的丧失。P700氧化还原瞬变动力学与血氧测定数据的比较表明，氧浓度是控制叶片和分离叶绿体中电子传输的关键因素。
