A KINETIC-ANALYSIS OF THE EFFECTS OF INHIBITOR-1 AND INHIBITOR-2 ON THE ACTIVITY OF PROTEIN PHOSPHATASE-1
A KINETIC-ANALYSIS OF THE EFFECTS OF INHIBITOR-1 AND INHIBITOR-2 ON THE ACTIVITY OF PROTEIN PHOSPHATASE-1
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DOI：
10.1111/j.1432-1033.1983.tb07363.x
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发表时间：
1983-01-01
期刊：
影响因子：
--
通讯作者：
COHEN, P
中科院分区：
文献类型：
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作者：
FOULKES, JG;STRADA, SJ;COHEN, P
[兔肌肉]蛋白磷酸酶-1及其2种抑制剂蛋白之间的稳态相互作用进行了研究，在体外低酶浓度的Michaelis-Menten方程的假设似乎是有效的。在这些条件下，并且在不存在二价阳离子的情况下，抑制剂-1表现为使用磷酸化酶a作为底物的混合抑制剂，而抑制剂-2是竞争性抑制剂。抑制剂-1和抑制剂-2不以相同的方式与蛋白磷酸酶-1相互作用。抑制剂-1在Mn 2+存在下仅为蛋白磷酸酶-1的底物，并且其去磷酸化被抑制剂-2（Kis = 8 nM）竞争性抑制。抑制剂-1在Mn 2+存在下不抑制其自身的去磷酸化。其作为底物的Km（190 nM）远高于其作为抑制剂的Ki（1.5-7.5 nM）。结果与蛋白磷酸酶-1上存在抑制剂-1的单一结合位点的模型一致，该结合位点不同于磷酸化酶a的结合位点。设想抑制剂-1与该位点的结合不仅抑制其它底物的去磷酸化，而且允许其磷酸苏氨酸接近负责其它底物的去磷酸化的相同催化基团。G-底物是一种专门在苏氨酸残基上磷酸化的蛋白质，它不抑制磷酸化酶a的去磷酸化，并且其去磷酸化被抑制剂-1或抑制剂-2有效抑制。根据这些结果，磷酸苏氨酸残基在抑制剂-1的作用进行了讨论。
The steady-state interaction between [rabbit muscle] protein phosphatase-1 and its 2 inhibitor proteins was studied in vitro at low enzyme concentrations where the assumptions of the Michaelis-Menten equation appeared to be valid. Under these conditions, and in the absence of divalent cations, inhibitor-1 behaved as a mixed inhibitor using phosphorylase a as a substrate, whereas inhibitor-2 was a competitive inhibitor. Inhibitor-1 and inhibitor-2 do not interact with protein phosphatase-1 in an identical manner. Inhibitor-1 was only a substrate for protein phosphatase-1 in the presence of Mn2+, and its dephosphorylation was inhibited competitively by inhibitor-2 (Kis = 8 nM). Inhibitor-1 did not inhibit its own dephosphorylation in the presence of Mn2+. Its Km as a substrate (190 nM) was very much higher than its Ki as an inhibitor (1.5-7.5 nM). The results are consistent with a model in which a single binding site for inhibitor-1 is present on protein phosphatase-1, distinct from the binding site for phosphorylase a. It is envisaged that the binding of inhibitor-1 to this site not only inhibits the dephosphorylation of other substrates but permits access of its phosphothreonine to the same catalytic group(s) responsible for the dephosphorylation of other substrates. G-substrate, a protein phosphorylated exclusively on threonine residues, did not inhibit the dephosphorylation of phosphorylase a and its dephosphorylation was potently inhibited by inhibitor-1 or inhibitor-2. The role of the phosphothreonine residue in inhibitor-1 is discussed in the light of these results.