Catalytic consequences of oligomeric organization: kinetic evidence for "tethered" acto-heavy meromyosin at low ATP concentrations.
Catalytic consequences of oligomeric organization: kinetic evidence for "tethered" acto-heavy meromyosin at low ATP concentrations.
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寡聚组织的催化后果：低 ATP 浓度下“束缚”的重肌球蛋白的动力学证据。
DOI：
10.1073/pnas.81.17.5345
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发表时间：
1984
影响因子：
11.1
通讯作者：
Clark,PK
中科院分区：
文献类型：
--
作者：
Hackney,DD;Clark,PK
肌球蛋白的超分子组织对ATP酶活性的影响进行了研究，在一个范围内的ATP浓度，作为模型系统亚片段1（S1）和重肌球蛋白（HMM），这分别是单体和二聚体的肌球蛋白的蛋白水解片段。在低ATP水平的存在下，在一个摩尔过量的肌动蛋白，二聚HMM显示出增加的ATP水解速率相对于单体S1。高浓度的ATP抑制了HMM ATP酶的增加，从而将acto-HMM ATP酶速率降低至较低的acto-S1水平。该观察结果与acto-HMM在低ATP下的快速ATP水解一致，这是由于从“栓系的”acto-HMM物质中快速释放产物，所述物质具有与一个头基结合的产物，而另一个头基保持与肌动蛋白结合。在高浓度的ATP下，ATP与两个头部基团结合，导致HMM与肌动蛋白的净解离。该模型得到了18 O交换数据的支持。Acto-HMM水解ATP，在高ATP水平下将水氧广泛交换成Pi，但在低ATP水平下不。Acto-S1在高和低ATP水平下均表现出广泛的交换。该结果与在低ATP下从栓系的acto-HMM中间体的快速产物释放一致。
The influence of the supramolecular organization of myosin on its ATPase activity was investigated at a range of ATP concentrations, using as a model system subfragment 1 (S1) and heavy meromyosin (HMM), which are respectively monomeric and dimeric proteolytic fragments of myosin. At low ATP levels in the presence of a molar excess of actin, dimeric HMM showed an increased rate of ATP hydrolysis relative to that for monomeric S1. This increased ATPase for HMM was inhibited by high concentrations of ATP, which reduced the acto-HMM ATPase rate to the lower level of acto-S1. This observation is consistent with the rapid ATP hydrolysis of acto-HMM at low ATP being due to rapid product release from a "tethered" acto-HMM species, which has product bound to one head group while the other head group remains bound to actin. At high concentrations of ATP, ATP binds to both head groups, resulting in net dissociation of HMM from actin. This model is supported by 18O exchange data. Acto-HMM hydrolyzed ATP with extensive exchange of water oxygens into Pi at high ATP levels, but not at low ATP levels. Acto-S1 exhibited extensive exchange at both high and low ATP levels. This result is consistent with rapid product release from a tethered acto-HMM intermediate at low ATP.