Amino acid sequence of a peptide containing an essential cysteine residue of Escherichia coli GMP synthetase.

The amino acid sequence of a 51-residue tryptic peptide of citraconylated [1-14C]carboxamidomethyl-labeled Escherichia coli GMP synthetase was determined by sequenator analyses of the intact peptide and fragments obtained by cleavage of the peptide with cyanogen bromide, trypsin, and Staphylcoccus aureus strain V8 protease. The cysteine residue of this peptide fragment is essential for glutamine-dependent GMP synthesis activity and is implicated in formation of a hypothetical covalent glutamyl-enzyme intermediate. There is essentially cysteine-containing regions of two other glutamine amidotransferases, Pseudomonas putida anthranilate synthetase Component II and chicken liver formylglycinamide ribonucleotide amidotransferase. There is, however, a cluster of amino acids with "antipathy" for helix formation and a "nonessential" cysteine of anthranilate synthetase Component II.