L-Phenylalanine: tRNA ligase of Escherichia coli K10. The effect of O replaced by S substitution on substrate and ligand binding properties of ATP.

The Km and V values of the tRNA-charging reaction have been measured for L-phenylalanine:tRNA ligase and the geometric isomers of adenosine 5'-O-(1-thio)triphosphate, adenosine 5'-O-(2-thio)triphosphate and for 5'-O-(3-thio)triphosphate. All ATP analogs were found to be substrates with values of Km similar or (up to 10-fold) higher, and with values of V in the range of 10--30% compared with the natural substrate. The dissociation constants of the binary enzyme-nucleotide and ternary enzyme-nucleotide-L-phenylalaninol complexes were analysed as a function of the position of the sulfur atom indicating those phosphate groups which are involved in an enzyme-triphosphate interaction. The results are consistent with a participation of the beta and gamma-phosphate in the binary complex formation and an additional interaction at the positions of the alpha and beta-phosphate groups in the ternary complexes.