CARBON-DIOXIDE STIMULATES PEROXYNITRITE-MEDIATED NITRATION OF TYROSINE RESIDUES AND INHIBITS OXIDATION OF METHIONINE RESIDUES OF GLUTAMINE-SYNTHETASE - BOTH MODIFICATIONS MIMIC EFFECTS OF ADENYLYLATION
Bs. Berlett et al., CARBON-DIOXIDE STIMULATES PEROXYNITRITE-MEDIATED NITRATION OF TYROSINE RESIDUES AND INHIBITS OXIDATION OF METHIONINE RESIDUES OF GLUTAMINE-SYNTHETASE - BOTH MODIFICATIONS MIMIC EFFECTS OF ADENYLYLATION, Proceedings of the National Academy of Sciences of the United Statesof America, 95(6), 1998, pp. 2784-2789
The activity of glutamine synthetase (EC 6.3.1.2) from Escherichia col
i is regulated by the cyclic adenylylation and deadenylylation of Tyr-
397 in each of the enzyme's 12 identical subunits. The nitration of Ty
r-397 or of the nearby Tyr-326 by peroxynitrite can convert the unaden
ylylated enzyme to a form exhibiting regulatory characteristics simila
r to the form obtained by adenylylation. The adenylylated conformation
can also be elicited by the oxidation of surface-exposed methionine r
esidues to methionine sulfoxide. However, the nitration of tyrosine re
sidues and the oxidation of methionine residues are oppositely directe
d 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 i
s stimulated and nitration of tyrosine is prevented, It was further es
tablished that adenylylation of Tyr-397 precludes its nitration by per
oxynitrite. Furthermore, nitration of Tyr-326 together with either nit
ration or adenylylation of Tyr-397 leads to inactivation of the enzyme
. These results demonstrate that CO2 can alter the course of peroxynit
rite-dependent reactions and serve notice that (i) the reactions have
physiological significance only if they are shown to occur at physiolo
gical concentrations of CO2 and physiological pH; and (ii) the peroxyn
itrite-dependent nitration of tyrosine residues or the oxidation of me
thionine residues of metabolically regulated proteins can seriously co
mpromise their biological function.