A Comparative Study of the Interactions of Escherichia coli Leucyl-, Seryl-, and Valyl-Transfer Ribonucleic Acid Synthetases with Their Cognate Transfer Ribonucleic Acids

Kinetic and equilibrium binding studies (enzyme-tRNA complex formation examined by gel filtration) were conducted in the same buffer with leucyl-tRNA synthetase and five tRNAleu isoacceptors, seryl-tRNA synthetase and three tRNAser isoacceptors, and valyl-tRNA synthetase and two tRNAval isoacceptors. All of the enzymes and tRNAs were highly purified from one strain of Escherichia coli K-12. The tRNA Km values and relative binding affinities are closely similar (estimates of ΔF range between 10 and 11 kcal per mole), suggesting that tRNA recognition by these three enzymes has some common thermodynamic feature. The results at least indicate basic similarities in the geometry of the aminoacyl-tRNA synthetase-tRNA complex. This notion is supported by the finding that all three enzymes exhibit a reaction sequence of the bi uni uni bi ping pong type, the addition order of substrates being amino acid, ATP, tRNA. The three enzymes differ in their susceptibility to ATP substrate inhibition.