PEROXYNITRITE-MEDIATED NITRATION OF TYROSINE RESIDUES IN ESCHERICHIA-COLI GLUTAMINE-SYNTHETASE MIMICS ADENYLYLATION - RELEVANCE TO SIGNAL-TRANSDUCTION

Treatment of Escherichia coli glutamine synthetase (GS) with peroxynit rite leads to nitration of some tyrosine residues and conversion of so me methionine residues to methionine sulfoxide (MSOX) residues, Nitrat ion, but not MSOX formation, is stimulated by Fe-EDTA. In the absence of Fe-EDTA, nitration of only one tyrosine residue per subunit of unad enylylated GS leads to changes in divalent cation requirement, pH-acti vity profile, affinity for ADP, and susceptibility to feedback inhibit ion by end products (tryptophan, AMP, CTP), whereas nitration of one t yrosine residue per subunit in the adenylylated GS leads to complete l oss of catalytic activity. In the presence of Fe-EDTA, nitration is a more random process: nitration of five to six tyrosine residues per su bunit is needed to convert unadenylylated GS to the adenylylated confi guration. These results and the fact that nitration of tyrosine residu es is an irreversible process serve notice that the regulatory functio n of proteins that undergo phosphorylation or adenylylation in signal transduction cascades might be seriously compromised by peroxynitrite- promoted nitration.