Glutamine active site of formylglycinamide ribonucleotide amidotransferase. 2. Amino acid sequence of labeled peptides.

The purification and characterization of two related peptides making up the glutamine binding site of formylglycinamide ribonucleotide amidotransferase from chicken liver have been presented. An amino acid residue(s) involved in binding glutamine to the enzyme was selectively labeled with [14C]iodoacetate. The labeled enzyme was reduced, carboxymethylated, and degraded by trypsin to a large radioactive peptide that yielded on acid hydrolysis only cysteine as a radioactive carboxymethylated derivative. The tryptic peptide was further digested with a protease from Streptomyces griseus. Two radioactive fractions (I and II) were obtained by gel filtration on Sephadex G-25. Furthermore, two 14C-containing peptides have been isolated from fraction I by the aid of ion exchange chromatography on AG 1-X2, AG 50W-X2 and DEAE-cellulose. Upon acid hydrolysis both peptides yielded only carboxymethylcysteine (CMCys), cystine, glycine, valine, aspartic acid, and glutamic acid. The partial sequences of the amino residues in these peptides, which are located at the glutamine binding site, have been established by the dansyl-Edman method. The sequences of amino acids of peptides a and b are Gly-Val-Cys([14C]CM)-Asp-Asx-Cys(CM)-Glx...and Gly-Val-Cys([14C]CM)-Asx-Asx..., respectively. The two peptides are undoubtedly derived from the same segment of the original protein.