was not functional, suggesting that the b subunit membrane spanning domain may have a

role in allowing the proton channel of the a and c subunits to align correctly (202). Here,

we demonstrated that mutation of only a single amino acid, at positions 2, 6 or 10

(basn24ala, bthr64ala Or bginlonala), did not significantly affect the function of the enzyme. In

fact, the minimal loss of enzyme activity associated from any of the single mutations did

not nearly add up to the total defect of all three mutations combined. The results support

the idea that although no single amino acid is necessary for the arrangement of a

functional proton channel, several sites contribute synergistically to the formation of a

functional F1Fo ATP synthase enzyme complex.

 In the tether region of the b subunit, Dr. Paul Sorgen had constructed a series of

insertions and deletions and observed that the altered b subunits were capable of forming

the peripheral stalk of a functional F1Fo ATP synthase complex (193, 194). It was not

known whether similar insertions or deletions could be accommodated in other regions of

the b subunit where crucial interactions with Fl subunits are believed to occur. Dr. Deepa

Bhatt observed that neither insertions nor deletions were tolerated in a small stretch of

hydrophobic amino acids found in the Fl binding domain, bl244130 (Figure 5-5). Four

amino acid insertions, as well as the corresponding deletions, scattered throughout the

remainder of the soluble portion of the b dimer were constructed by Stephanie Cole and

Megan Greenlee and were found to result in a functional F1Fo ATP synthase complex

(Figure 5-5). In the present chapter, we confirmed that a four amino acid truncation at

the extreme carboxyl terminus of the b subunit (bal534end) results in a partially assembled

defective enzyme complex. However, duplication of the last four amino acids (b+153-156)

had no appreciable affect on enzyme assembly or function.