THE F-0 COMPLEX OF THE ESCHERICHIA-COLI ATP SYNTHASE - INVESTIGATION BY ELECTRON SPECTROSCOPIC IMAGING AND IMMUNOELECTRON MICROSCOPY

Cholate-solubilized F-0 complexes of the ATP synthase (F0F1) from Esch erichia coli were studied by application of conventional transmission electron microscopy and electron spectroscopic imaging (ESI) of negati vely stained samples. Using the ESI mode, the structural organization of the F-0 complex (diameter of 7.5 +/- 0.5 nm) could be observed in m ore detail and defined projections could be distinguished. Projection A appears as a deltoid-like structure with bilateral symmetry. Project ion B has an overall trapezoidal shape with some similarity in shape t o the letter W. Applying the ESI mode to the ac complex dissolved in c holate-containing buffer, an elongated structure consisting of two int ensity maxima could be observed. Simulations with models of the F-0 an d the ne complex revealed that the projections observed can be obtaine d by tilting and rotating a model in which subunit a and the two copie s of subunit b are located outside the subunit c oligomer. This view o f structural organization was supported by results obtained with F-0 c omplexes decorated with monoclonal antibodies against subunits a, b or c.