Interaction of crystalline tyrosyl-tRNA synthetase with adenosine, adenosine monophosphate, adenosine triphosphate and pyrophosphate in the presence of tyrosinol.

Crystalline complexes of tyrosyl-tRNA synthetase from Bacillus stearothermophilus were prepared with adenosine, AMP, ATP and PPi, all in the presence of tyrosinol, which binds strongly to the tyrosine binding site but cannot be adenylated by ATP. The hydrolysis of ATP in the presence of crystalline tyrosyl-tRNA synthetase (or redissolved crystals) was checked in the absence of tyrosine or with tyrosinol. No ATPase activity due to the enzyme was detected under these conditions. Difference Fourier analysis shows that tyrosinol binds to the tyrosine binding site with the same occupancy as the amino acid. Comparison between tyrosine and tyrosinol shows the location of the extra oxygen atom of the tyrosine carboxylate. Adenosine, AMP and ATP are weakly bound to the enzyme in the presence of tyrosinol. Even when ATP is present at a concentration greater than Km for adenylation, it is not sufficiently strongly bound to give a recognizable density for adenine. However, some significant peaks of density are present near the tyrosine binding site. One of them is at the usual ribose binding site, and may possibly represent ribose binding with a low occupancy. When AMP is bound a similar but not identical arrangement of density is observed.