l‐Phenylalanine: tRNA Ligase of Escherichia coli K10

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Abstract
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 β and γ‐phosphate in the binary complex formation and an additional interaction at the positions of the α and β‐phosphate groups in the ternary complexes.