a complete loss of enzyme function. The b subunit dimer was not found in membranes

when cells expressed only the b+124-130 Subunit. Heterodimerization was detected in cells

expressing either arg36 mutation, barg36 ile-V5 Or barg36 glu-V5, with bwt-his, bal534end-his/bwt-

vs and b+124-130-his/bwt-v5 (Figure 3-10).

 Dimerization was also observed in membrane preparations from cells expressing

both bal534end-his/barg364ile-V5 and bAl534end-his/barg364glu-V5. More importantly, enzyme

complexes incorporated with the mutant heterodimers were functionally active,

suggesting that each of the b subunits were complementing the other to form an intact

and functional enzyme complex. This observation demonstrated unambiguously that

F1Fo ATP synthase complexes containing b heterodimers were active and provided

evidence that each of the individual b subunits provide specialized functions within the

peripheral stalk. Clearly, each of the mutant b subunits compensates for what the other is

lacking.

 The work accomplished in this chapter raises a question concerning the relative

positions of the individual b subunits of the peripheral stalk. In order for F1Fo ATP

synthase containing the two different mutant b subunits to be intact and functional, it is

likely that the barg364ile-V5 (Or barg364glu-V5) Subunit must be positioned such that its

extreme C-terminus forms the appropriate contacts with the 6 subunit of F1. Similarly,

the bAl534end-his subunit must be positioned so that its barg36 makes the appropriate contacts

with the Fo subunits (Figure 3-11). Incorrect positioning of the mutant b subunits during

assembly might be expected to lead to an inactive or partially assembled enzyme

complex. An answer to this question will be a goal discussed in "Future Directions".