Photophosphorylation in intact algae : Effects of inhibitors, intensity of light, electron acceptor and donors
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概要
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The luciferin-luciferase method was used to determine ATP extracted from dark-maintained and light-exposed samples of the green alga Chlorella pyrenoidosa and of the blue-green alga Anacystis nidulans. A few measurements on Synechococcus lividus (a blue-green thermophile, clone 65℃) are also reported. 1 . The light-minus-dark ATP levels (ΔATP) from aerobic cells of Chlorella and Anacystis were negative; however, ΔATP from Synechococcus was positive. Large positive ΔATP was obtained in regularly grown (RG : moderate light) Chlorella treated with oligomycin; dark levels were reduced, light levels remained essentially unaffected. In high-light exposed (HLE) Chlorella, oligomycin reduced both light and dark ATP levels, but positive ΔATP was still obtained. However, in Anacystis, which has a different organization of thylakoid membrane, oligomycin severely reduced both the light and the dark ATP levels and the ΔATP remained negative. 2. The oligomycin ( 12 μM) treated Chlorella and the untreated Anacystis and ,Synechococcus show the presence of cyclic photophosphorylation under conditions in which the non-cyclic electron flow from photosystem II to photosystem I is blocked by 10 μM 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), or not allowed to operate by the absence of CO_2. Cyclic photophosphorylation ranged from 10-30% of the maximum ΔATP in RG, to 40-50% in HLE Chlorella. In RG Chlorella, cyclic and non-cyclic (in the absence of DCMU) photophosphorylation (ΔATP) saturate at about 10^3 ergs cm^<-2> sec^<-1> and 10^4 ergs cm^<-2> sec^<-1> red ( >640 nm) light, respectively; a lag was observed in the light curve. 3. In Chlorella, the addition of the photosystem I electron acceptor methyl viologen (MV; 1 mM) increased ΔATP by twofold. Further addition of DCMU (25 μM) reduced this to the level observed with DCMU alone. If 1 mM reduced dichlorophenol indophenol or phenazine methosulphate (DCPIPH_2 or PMSH_2, respectively) was added along with DCMU, the ΔATP level was 30-40% of the control. Further addition of MV increased the ΔATP to be 70-80% of that of the control. These and other results confirm the presence of both non-cyclic and cyclic photophosphorylation in vivo, the former predominating in Chlorella, and the latter in Anacystis and Synechococcus.
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