In the Figure, a transparent monomeric bc1 complex (abstracted from the chicken mitochondrial complex, 1bcc, appropriately scaled, and viewed down the vertical axis with respect to the membrane plane) is superimposed on the array taken from Fig. 4B of the Jungas et al. paper, and positioned in the widest gap in the array.
- Assuming that this abstracted complex is a good model for the bacterial monomeric complex, the cross-sectional area in the membrane-spanning region of cyt b would barely fit between the outer diffraction map contours, and only if the anchoring helices of ISP and cyt c1 could be accommodated in more open slots, for example the openings of the two opposing "C"s.
- Although the gap might possibly accommodate the bc1 complex monomer, the projection map provides no evidence for such an occupancy, since it shows too little material in the gap.
- It is not clear how the contours derived from optical analysis of negatively stained images relate to protein volume in the membrane, but the models all have the LH1 helices more or less vertical, with a fairly uniform diameter for the resulting cylinder. Presumably there are protein contacts between the elements of the array; if so, the contours underestimate the volume.
- Whatever the orientation, positioning of a bc1 complex monomer as shown in the Fig. would lead to a marked asymmetry with respect to distances between the Qo site, where QH2 is oxidized in cyt b, and each of the reaction center QB sites where QH2 is generated, since one of these would be on the wrong side of the RC/LH1 dimer.
- The kinetics of turnover of the high potential chain following flash activation are the same in pufX- strains (in which the RC/LH1 dimer is not seen) as in wild type. It seems unlikely that the interactions necessary to form a supercomplex would have the same tight association expected if the interface was so dramatically altered.