Second stalk of ATP synthase - Cross-linking of gamma subunit in F-1 to truncated F(o)b subunit prevents ATP hydrolysis

ATP synthase consists of two portions, F-1 and F-o, connected by two stalks : a central rotor stalk containing gamma and epsilon subunits and a periphe ral, second stalk formed by delta and two copies of F(o)b subunits. The sec ond stalk is expected to keep the stator subunits from spinning along with the rotor. We isolated a TF1-b'(2) complex (alpha (3)beta (3)gamma delta ep silonb'(2)) of a thermophilic Bacillus PS3, in which b' was a truncated cyt oplasmic fragment of F(o)b subunit, and introduced a cysteine at its N term inus (bc'). Association of b'(2) or bc'(2) with TF1 did not have significan t effect on ATPase activity. A disulfide bond between the introduced cystei ne of bc' and cysteine 109 of gamma subunit was readily formed, and this cr oss-link caused inactivation of ATPase. This implies that F(o)b subunit bou nd to stator subunits of F-1 with enough strength to resist rotation of gam ma subunit and to prevent catalysis. Contrary to this apparent tight bindin g, some detergents such as lauryldodecylamine oxide tend to cause release o f b'(2) from TF1.