Milgrom Y M, Cross R L
Department of Biochemistry and Molecular Biology, State University of New York Health Science Center, Syracuse 13210.
J Biol Chem. 1993 Nov 5;268(31):23179-85.
We have studied the properties of beef heart mitochondrial F1 having inhibitory MgADP bound at one of the three catalytic sites and various levels of occupancy of the three noncatalytic nucleotide sites including zero, two, or three ADP/ATPs or two ADP/ATP plus one GTP. The properties examined include the rate of MgATP-dependent reactivation and the rate of increase in the fraction of F1 containing transiently bound intermediates. For each form of the enzyme tested, the rate of reactivation closely paralleled the rate of increase in the level of bound intermediates, indicating that when one catalytic site on F1 is blocked by inhibitory MgADP, the remaining two sites are incapable of residual uni- or bi-site activity. It was also found that the stability of the MgADP-inhibited complex decreases with full occupancy of the noncatalytic sites. This demonstrates that the noncatalytic sites modulate the properties of catalytic sites. Finally, it was found that the noncatalytic sites on mitochondrial F1 do not, as has long been believed, bind adenine nucleotides exclusively. Evidence is presented that both GTP and PPi bind tightly at noncatalytic sites.
我们研究了牛肉心线粒体F1的特性，其中一个催化位点结合了抑制性MgADP，三个非催化核苷酸位点存在不同程度的占据情况，包括零、两个或三个ADP/ATP，或两个ADP/ATP加一个GTP。所检测的特性包括MgATP依赖性再激活速率以及含有瞬时结合中间体的F1部分增加的速率。对于所测试的每种酶形式，再激活速率与结合中间体水平的增加速率密切平行，这表明当F1上的一个催化位点被抑制性MgADP阻断时，其余两个位点无法进行残余的单位点或双位点活性。还发现，随着非催化位点被完全占据，MgADP抑制复合物的稳定性降低。这表明非催化位点调节催化位点的特性。最后，发现线粒体F1上的非催化位点并不像长期以来所认为的那样仅结合腺嘌呤核苷酸。有证据表明，GTP和PPi都紧密结合在非催化位点上。
