ENERGY SUPPLY FOR ATP-SYNTHASE DEFICIENT CHLOROPLASTS OF CHLAMYDOMONAS REINHARDII

The mutant F54 of the unicellular green alga Chlamydomonas reinhardii is not able to perform photophosphorylation. Nevertheless, it grows on acetate and the chloroplasts accomplish most of their energy-requirin g synthetic processes. However, no light-dependent chloroplast protein synthesis could be detected in intact F54 chloroplasts isolated from a cell wall-deficient double mutant F54.cw-15. Exogenous ATP was not a ble to induce this in organello protein synthesis to an appreciable de gree. In contrast, the strictly ATP-dependent protein synthesis was st imulated very efficiently by glyceraldehyde-3-phosphate, dihydroxyacet one phosphate and glycerol-3-phosphate, but strongly inhibited by 3-ph osphoglycerate. These compounds can be transported across the envelope membrane by the triose phosphate translocator. Pyridoxal phosphate, a specific inhibitor of the translocator, abolished the stimulation by triose phosphates. Spermidine, which activates initiation of translati on in chloroplasts, enhanced triose phosphate-stimulated protein synth esis even further. In the dark, no stimulation was observed, indicatin g that a light-dependent reaction was also involved in this kind of AT P production in chloroplasts. The results suggest that chloroplasts de fective in photophosphorylation recruit their energy via an ATP shuttl e which was shown in this study to import rather than export ATP acros s the chloroplast envelope.