Figure 4. Model for proton translocation.
(A and B) The a subunit (green), along with the membrane-intrinsic α-helices of the b subunit (red), form two clusters that could be the half channels needed for trans-membrane proton translocation. (C and D) The map segment corresponding to the c8-ring is shown for state 2a (pink) and state 2c (purple). The difference in rotational position of the c-ring is consistent with the Brownian fluctuations predicted for the generation of a net rotation. Scale bar, 25 Å.