Photophosphorylation in intact algae: Effects of inhibitors, intensity of light, electron acceptor and donors

The luciferin-luciferase method was used to determine ATP extracted from darkmaintained 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 bluegreen thermophile, clone 65°C) are also reported. 1. The light-minus-dark ATP levels (JATP) from aerobic cells of Chlorella and Anacystis were negative; however, JATP from Synechococcus was positive. Large positive JATP 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 A ATP 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 JATP remained negative. 2. The oligomycin (12 fit*) 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 f*M 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU), or not allowed to operate by the absence of CO2. Cyclic photophosphorylation ranged from 10-30% of the maximum JATP in RG, to 40-50% in HLE Chlorella. In RG Chlorella, cyclic and non-cyclic (in the absence of DCMU) photophosphorylation (JATP) saturate at about 10 ergs cm" sec" and 10 ergs cmsec" 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 nut) increased JATP by twofold. Further addition of DCMU (25 ^M) reduced this to the level observed with DCMU alone. If 1 mil reduced dichlorophenol indophenol or phenazine methosulphate (DCPIPH2 or PMSH2, respectively) was added along with DCMU, the JATP level was 30-40% of the control. Further addition of MV increased the JATP 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.