CONFORMATIONAL CHANGE OF MAMMALIAN TYROSYL-TRANSFER-RNA SYNTHETASE INDUCED BY TYROSYL ADENYLATE FORMATION

The fluorescent probe 1,5-I-AEDANS was covalently attached to bovine t yrosyl-tRNA synthetase outside of enzyme active site in a nearly stoic hiometric amount (2 probe molecules per enzyme dimer). Singlet-singlet resonance energy transfer has been used for the measurement of the ap parent distance between tryptophan residues of enzyme and covalently a ttached 1,5-I-AEDANS. This distance was estimated as 27.4 Angstrom in the assumption of the random orientation of the donor and acceptor flu orophores. Tyrosyl adenylate formation catalyzed by bovine tyrosyl-tRN A synthetase resulted in the highly specific enhancement of 1,5-I-AEDA NS fluorescence and concomitant decrease the apparent distance between the probe and tryptophanyls to 22.3 - 25.7 Angstrom. These results ar e consistent with the conformational change of tyrosyl-tRNA synthetase during tyrosyl adenylate formation which propagates to distant from a ctive site regions of enzyme structure.