Rosing J, Harris D A, Slater E C, Kemp A
J Supramol Struct. 1975;3(3):284-96. doi: 10.1002/jss.400030311.
The tightly bound nucleotides of the beff-heart mitochondrial ATPase are released during cold inactivation followed by ammonium sulfate precipitation. During incubation at 0 degrees C the sedimentation coefficient (S20W) of the ATPase first declines from 12.1S to 9S. Prolonged incubation or precipitation with ammonium sulfate leads to dissociation of the 9S component into subunits with S20W of 3.5S. The 9S component still bears bound nucleotides which exchange more extensively and rapidly with added nucleotides than those bound to the active 12.1S component. The bound nucleotides are lost when the 9S form dissociates into the smaller subunits. Thus, firm binding of nucleotides is a property of the quarternary structure of the enzyme. The exchangeability of the nucleotides bound to the ATPase of chloroplast membranes is greatly increased in membranes illuminated in the presence of pyocyanine. Pi can exchange into both the beta and gamma positions of the bound nucleotides when the membranes are energized in the presence of Mg2+. The exchange of the nucleotides and the incorporation of Pi are insensitive to the inhibitor Dio-9 but are inhibited by the uncoupler S13. This inhibition by S13 parallels that of the inhibition of photosynthetic phosphorylation. These findings are discussed with regard to our hypothesis that electron transfer causes release of preformed tightly bound ATP from the ATPase by inducing a conformational change.
在冷失活后紧接着硫酸铵沉淀的过程中，牛肉心线粒体ATP酶紧密结合的核苷酸会被释放出来。在0℃孵育期间，ATP酶的沉降系数（S20W）首先从12.1S降至9S。长时间孵育或用硫酸铵沉淀会导致9S组分解离成沉降系数为3.5S的亚基。9S组分仍然带有结合的核苷酸，这些核苷酸与添加的核苷酸相比，与活性12.1S组分结合的核苷酸交换更广泛、更迅速。当9S形式解离成较小的亚基时，结合的核苷酸会丢失。因此，核苷酸的牢固结合是该酶四级结构的一个特性。在存在绿脓菌素的光照下，叶绿体膜结合的ATP酶所结合核苷酸的交换能力大大增强。当膜在Mg2+存在下被激活时，Pi可以交换到结合核苷酸的β和γ位置。核苷酸的交换和Pi的掺入对抑制剂Dio-9不敏感，但被解偶联剂S13抑制。S13的这种抑制作用与光合磷酸化的抑制作用相似。根据我们的假设，即电子传递通过诱导构象变化导致预先形成的紧密结合的ATP从ATP酶中释放出来，对这些发现进行了讨论。
