Portal de Periódicos da CAPES

Chloroplast ATP synthase contains one single copy of subunit δ that is indispensable for photophosphorylation

1989; Wiley; Volume: 179; Issue: 1 Linguagem: Inglês

10.1111/j.1432-1033.1989.tb14528.x

1432-1033

Siegfried Engelbrecht, Karin Schürmann, Wolfgang Junge,

Photosynthetic Processes and Mechanisms

F 0 F 1 ATP synthases synthesize ATP in their F 1 portion at the expense of free energy supplied by proton flow which enters the enzyme through their channel portion F 0 . The smaller subunits of F 1 , especially subunit δ, may act as energy transducers between these rather distant functional units. We have previously shown that chloroplast δ, when added to thylakoids partially depleted of the coupling factor CF 1 , can reconstitute photophosphorylation by inhibiting proton leakage through exposed coupling factor CF 0 . In view of controversies in the lieterature, we reinvestigated two further aspects related to subunit δ, namely (a) its stoichiometry in CF 0 CF 1 and (b) whether or not δ is required for photophosphorylation. By rocket immunoelectrophoresis of thylakoid membrances and calibration against purified δ, we confirmed a stoichiometry of one δ per CF 0 CF 1 . In CF 1 ‐depleted thylakoids photophosphorylation could be reconstituted not only by adding CF 1 and subunit δ but, surprisingly, also by CF 1 (−δ). We found that the latter was attributable to a contamination of CF 1 (−δ) preparations with integral CF 1 . To Lesser extent CF 1 (−δ) acted by complementary rebinding to CF 0 channels that were closed because they contained δ [CF 0 (+δ)]. This added catalytic capacity to proton‐tight thylakoid vesicles. The ability of subunit δ to control proton flow through CF 0 and the absolute requirement for δ in restoration of photophosphorylation suggest an essential role of this small subunit at the interface between the large portions of ATP synthase: δ may be part of the couping site between electrochemical, conformational and chemical events in this enzyme.