Berlett B S, Levine R L, Stadtman E R
Laboratory of Biochemistry, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-0342, USA.
Proc Natl Acad Sci U S A. 1998 Mar 17;95(6):2784-9. doi: 10.1073/pnas.95.6.2784.
The activity of glutamine synthetase (EC 6.3.1.2) from Escherichia coli is regulated by the cyclic adenylylation and deadenylylation of Tyr-397 in each of the enzyme's 12 identical subunits. The nitration of Tyr-397 or of the nearby Tyr-326 by peroxynitrite can convert the unadenylylated enzyme to a form exhibiting regulatory characteristics similar to the form obtained by adenylylation. The adenylylated conformation can also be elicited by the oxidation of surface-exposed methionine residues to methionine sulfoxide. However, the nitration of tyrosine residues and the oxidation of methionine residues are oppositely directed by the presence and absence of CO2. At physiological concentrations of CO2, pH 7.4, nitration occurs but oxidation of methionine residues is inhibited. Conversely, in the absence of CO2 methionine oxidation is stimulated and nitration of tyrosine is prevented. It was further established that adenylylation of Tyr-397 precludes its nitration by peroxynitrite. Furthermore, nitration of Tyr-326 together with either nitration or adenylylation of Tyr-397 leads to inactivation of the enzyme. These results demonstrate that CO2 can alter the course of peroxynitrite-dependent reactions and serve notice that (i) the reactions have physiological significance only if they are shown to occur at physiological concentrations of CO2 and physiological pH; and (ii) the peroxynitrite-dependent nitration of tyrosine residues or the oxidation of methionine residues of metabolically regulated proteins can seriously compromise their biological function.
来自大肠杆菌的谷氨酰胺合成酶（EC 6.3.1.2）的活性受该酶12个相同亚基中每个亚基的Tyr-397的环腺苷酸化和去腺苷酸化调节。过氧亚硝酸盐对Tyr-397或附近的Tyr-326进行硝化，可将未腺苷酸化的酶转化为一种具有类似于腺苷酸化形式的调节特性的形式。腺苷酸化构象也可由表面暴露的甲硫氨酸残基氧化为甲硫氨酸亚砜引发。然而，酪氨酸残基的硝化和甲硫氨酸残基的氧化受二氧化碳的存在与否的相反调控。在生理浓度的二氧化碳、pH 7.4条件下，硝化反应发生，但甲硫氨酸残基的氧化受到抑制。相反，在没有二氧化碳的情况下，甲硫氨酸氧化受到刺激，酪氨酸硝化被阻止。进一步确定，Tyr-397的腺苷酸化可防止其被过氧亚硝酸盐硝化。此外，Tyr-326的硝化以及Tyr-397的硝化或腺苷酸化都会导致酶失活。这些结果表明，二氧化碳可以改变过氧亚硝酸盐依赖性反应的进程，并提醒人们：（i）只有当这些反应在生理浓度的二氧化碳和生理pH下发生时，它们才具有生理意义；（ii）过氧亚硝酸盐依赖性的代谢调节蛋白酪氨酸残基的硝化或甲硫氨酸残基的氧化会严重损害其生物学功能。
