5′-Adenylyl-O-tyrosine

Abstract A decapeptide containing 1 eq of adenylyl groups bound in phosphodiester linkage has been isolated in high yield from adenylylated glutamine synthetase. The decapeptide has the following amino acid composition: (Asp2, Glu2, Pro3, Gly1, Leu1, Tyr1). Tyrosine is the only amino acid present that could yield a phosphodiester derivative having the stability characteristics of the adenylylated peptide. Evidence that the adenylyl group is in fact bound in phosphodiester linkage to the phenolic hydroxyl group of tyrosine was obtained by comparing the ultraviolet absorption spectra of adenylylated and unadenylylated peptides at alkaline pH. A spectral peak, attributable to ionization of tyrosine hydroxyl groups, was absent in the adenylylated peptide, but became apparent when the adenylyl residues were removed with snake venom phosphodiesterase. The results suggest that a unique tyrosyl residue in glutamine synthetase is the site of adenylylation of the enzyme.