Hoppe J, Friedl P, Schairer H U, Sebald W, von Meyenburg K, Jørgensen B B
Department of Stoffwechselregulation, GBF-Gesellschaft für Biotechnologische Forschung mbH., Braunschweig-Stöckheim, FRG.
EMBO J. 1983;2(1):105-10. doi: 10.1002/j.1460-2075.1983.tb01389.x.
The accessibility of the three F0 subunits a, b and c from the Escherichia coli K12 ATP synthase to various proteases was studied in F1-depleted inverted membrane vesicles. Subunit b was very sensitive to all applied proteases. Chymotrypsin produced a defined fragment of mol. wt. 15,000 which remained tightly bound to the membrane. The cleavage site was located at the C-terminal region of subunit b. Larger amounts of proteases were necessary to attack subunit a (mol. wt. 30,000). There was no detectable cleavage of subunit c. It is suggested that the major hydrophilic part of subunit b extends from the membrane into the cytoplasm and is in contact with the F1 sector. The F1 sector was found to afford some protection against proteolysis of the b subunit in vitro and in vivo. Protease digestion had no influence on the electro-impelled H+ conduction via F0 but ATP-dependent H+ translocation could not be reconstituted upon binding of F1. A possible role for subunit b as a linker between catalytic events on the F1 component and the proton pathway across the membrane is discussed.
在去除F1的反向膜囊泡中，研究了大肠杆菌K12 ATP合酶的三个F0亚基a、b和c对各种蛋白酶的可及性。亚基b对所有应用的蛋白酶都非常敏感。胰凝乳蛋白酶产生了一个分子量为15,000的特定片段，该片段仍紧密结合在膜上。切割位点位于亚基b的C末端区域。攻击亚基a（分子量30,000）需要更多量的蛋白酶。未检测到亚基c的切割。有人认为，亚基b的主要亲水部分从膜延伸到细胞质中，并与F1部分接触。发现F1部分在体外和体内对b亚基的蛋白水解提供了一定的保护。蛋白酶消化对通过F0的电驱动H+传导没有影响，但在结合F1后无法重建ATP依赖的H+转运。讨论了亚基b作为F1组分上催化事件与跨膜质子途径之间连接物的可能作用。
