Effects of protein RNase inhibitor and substrate on the quaternary structures of bovine seminal RNase.
Effects of protein RNase inhibitor and substrate on the quaternary structures of bovine seminal RNase.
复制标题
蛋白质RNase抑制剂和底物对牛精液RNase四级结构的影响。
作者：
B. Satyanarayana Murthy;Claudia De Lorenzo;R. Piccoli;Giuseppe D'Alessio;Ravi Sirdeshmukh
蛋白质RNA酶抑制剂（PRI）对牛精液RNA酶（BS-RNA酶）活性的影响使用早先报道的酶的分离的四级形式MxM和M=M进行研究[Piccoli，R.，例如，等人（1992）Proc. Acad. Sci. U.S.A. 89，1870-1874]。我们发现，该抑制剂不与完整的分离形式，但有显着的，差异的影响时，在还原条件下进行测定的两种形式。这些条件对于抑制剂的完全活性是必需的，并且是其胞质定位的典型条件，也促进M=M形式的单体化，而在相同条件下，MxM形式变成非共价二聚体（NCD）。因此，在还原条件下BS-RNase或分离的季铵形式的敏感性似乎与两种形式的酶的差异单体化有关;单体对PRI敏感。本研究还表明，在平衡的两种形式之间的相互转换发生在还原环境中的速率要高得多，PRI进一步影响的相互转换，并改变有利于单体化的蛋白质的平衡。底物对两种形式之间的平衡起到相反的作用，发现底物稳定了蛋白质的NCD形式，两种形式之间的平衡向二聚体移动。这些结果是根据在胞质溶胶中发挥的酶的抗肿瘤作用进行分析的，即，在容纳PRI和核糖体RNA的隔室中，核糖体RNA是酶的分子靶标。
The effect of the protein RNase inhibitor (PRI) on the activity of bovine seminal RNase (BS-RNase) was investigated using the isolated quaternary forms, MxM and M=M, of the enzyme reported earlier [Piccoli, R., et al., (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 1870-1874]. We found that the inhibitor does not interact with the intact isolated forms but has dramatic, differential effects on the two forms when the assays are performed under reducing conditions. These conditions, which are essential for full activity of the inhibitor, and are typical of its cytosolic localization, also promote monomerization of the M=M form, while under identical conditions the MxM form becomes a noncovalent dimer (NCD). The sensitivity of BS-RNase or that of the isolated quaternary forms under reducing conditions thus appears to be related to differential monomerization of the two forms of the enzyme; monomer being sensitive to PRI. The present study also shows that the interconversion between the two forms in equilibrium occurs at much higher rates in a reducing environment and that PRI further affects the interconversion and alters the equilibrium favoring monomerization of the protein. An opposite effect on the equilibrium between the forms is played by the substrate, which is found to stabilize the NCD form of the protein with a shift in the equilibrium between the two forms towards the dimer. These results are analyzed in the light of the antitumor action of the enzyme which is exerted in the cytosol, i.e., in the compartment housing the PRI and the ribosomal RNA, the molecular target of the enzyme.