[The role of hydroxyl groups of tyrosine residues in RNA-ligase].

The stability of the AMP-RNA-ligase complex was studied. The complex was found to be stable for at least two weeks upon storage at 0 degrees. Approximately 50% of the initial radioactivity was retained after storage at 9 degrees for 49 days. The formation of adenosine in the complex decomposition products suggested the possible involvement of the tyrosine hydroxyl group in the formation of AMP-RNA-ligase complexes. In order to study the structure of the enzyme active site, the hydroxyl groups of the RNA-ligase tyrosine residues were modified with N-acetyl-imidazole. It was found that four out of 25 tyrosine residues are exceptionally susceptible to chemical modification with resultant complete suppression of the enzyme ability to form a complex with ATP. The kinetic parameters (Km, V) of native and modified RNA-ligase were determined and compared. A hypothetical scheme of the tyrosine hydroxyl group participation in RNA-ligase-catalyzed reactions is proposed.