Sinclair J, Sarai A, Garland S
Biochim Biophys Acta. 1979 May 9;546(2):256-69. doi: 10.1016/0005-2728(79)90044-6.
A study was made with a modulated oxygen electrode of the effect of variations of oxygen concentration on photosynthetic oxygen evolution from algal cells. When Chlorella vulgaris is examined with a modulated 650 nm light at 22 degrees C, both the oxygen yield and the phase lag between the modulated oxygen signal and the light modulations have virtually constant values between 800 and 120 ergs . cm-1 . s-1 if the bathing medium is in equilibrium with the air. Similar results are obtained at 32 degrees C between 1600 and 120 ergs . cm-2 . s-1. Under anaerobic conditions both the oxygen yield and the phase lag decrease if the light intensity is lowered below about 500 ergs . cm-2 . s-1 at 22 degrees C or about 1000 ergs . cm-2 . s-1 at 32 degrees C. A modulated 706 nm beam also gives rise to these phenomena but only at significantly lower rates of oxygen evolution. The cells of Anacystis nidulans and Porphyridium cruentum appear to react in the same way to anaerobic conditions as C. vulgaris. An examination of possible mechanisms to explain these results was performed using a computer simulation of photosynthetic electron transport. The simulation suggests that a backflow of electrons from a redox pool between the Photosystems to the rate-limiting reaction between Photosystem II and the water-splitting act can cause a decrease in oxygen yield and phase lag. If the pool between the Photosystems is in a very reduced state a significant cyclic flow is expected, whereas if the pool is largely oxidized little or no cyclic flow should occur. It is shown that the effects of 706 nm illumination and removal of oxygen can be interpreted in accordance with these proposals. Since a partial inhibition of oxygen evolution by 3-(3.4-dichlorophenyl)-1,1-dimethylurea (10(-8) M) magnifies the decreases in oxygen yield and phase lag, it is proposed that the pool which cycles back electrons is in front of the site of 3-(3,4-dichlorophenyl)-1,1-dimethylurea inhibition and is probably the initial electron acceptor pool after Photosystem II.
利用调制氧电极研究了氧浓度变化对藻类细胞光合放氧的影响。当在22℃用调制的650nm光照射普通小球藻时，如果培养液与空气平衡，在800至120尔格·厘米⁻¹·秒⁻¹之间，氧产量以及调制氧信号与光调制之间的相位滞后实际上都保持恒定值。在32℃，在1600至120尔格·厘米⁻²·秒⁻¹之间可得到类似结果。在厌氧条件下，如果在22℃光强降至约500尔格·厘米⁻²·秒⁻¹以下或在32℃降至约1000尔格·厘米⁻²·秒⁻¹以下，氧产量和相位滞后都会降低。一束调制的706nm光束也会引发这些现象，但氧释放速率明显更低。集胞藻和紫球藻细胞对厌氧条件的反应似乎与普通小球藻相同。利用光合电子传递的计算机模拟对解释这些结果的可能机制进行了研究。模拟表明，电子从光系统之间的氧化还原池回流到光系统II与水裂解反应之间的限速反应会导致氧产量和相位滞后降低。如果光系统之间的池处于非常还原的状态，预计会有显著的循环流动，而如果池大部分被氧化，则应很少或不发生循环流动。结果表明，706nm光照和去除氧的影响可以根据这些提议来解释。由于3-(3,4-二氯苯基)-1,1-二甲基脲（10⁻⁸M）对氧释放的部分抑制会放大氧产量和相位滞后的降低，因此有人提出，使电子循环回流的池位于3-(3,4-二氯苯基)-1,1-二甲基脲抑制位点之前，可能是光系统II之后的初始电子受体池。
