Enzyme complexes with a bAl534end-his WeTO found to be only partially assembled.

Thirdly, insertions and deletions in a hydrophobic stretch of amino acids in the b subunit

corresponding to amino acids 124-130 (VAILAVA) resulted in a complete loss of

enzyme function. The b 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-1 5 Or barg36-glu-1 5, with bwt-his, bAl534end-his/bwt-1-s and b+124-130-his/bwt-V5

(Figure 3-10).

















 arg36--ile-V5 1)
 S "wt-vS bwt-vS
 arg30-glu-V5 b+2-3-i
 b ^153~S--+end-his +2-3-i
 w-h is


Figure 3-10. Interactions of defective b subunit with wild type b subunits found in intact
 F1Fo ATP synthase complexes. An epitope-tag system was used in order to
 determine if a defective b subunit could form a dimer with a wild type b
 subunit. A V5 epitope tag was constructed at the C-terminus of the b subunit
 (shown in red) or a histidine epitope tag was placed at the N-terminus of the b
 subunit. Four mutant b subunits were studied and all were found to form a
 dimer with a wild type b subunit (1) barg36-ile-1 5, (2) barg36-glu-1 5, (3)
 bAl53-end-his and (4) b+124-130-his.