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Elongation factor (EF) Tu promotes the binding of aminoacyl-tRNA (aa-tRNA) to the acceptor site of the ribosome. This process requires the formation of a ternary complex (EF-Tu·GTP·aa-tRNA). EF-Tu is released from the ribosome as an EF-Tu·GDP complex. Exchange of GDP for GTP is carried out through the formation of a complex with EF-Ts (EF-Tu·Ts). Mammalian mitochondrial EF-Tu (EF-Tumt) differs from the corresponding prokaryotic factors in having a much lower affinity for guanine nucleotides. To further understand the EF-Tumt subcycle, the dissociation constants for the release of aa-tRNA from the ternary complex (K tRNA) and for the dissociation of the EF-Tu·Tsmt complex (K Ts) were investigated. The equilibrium dissociation constant for the ternary complex was 18 ± 4 nM, which is close to that observed in the prokaryotic system. The kinetic dissociation rate constant for the ternary complex was 7.3 × 10 4 s 1, which is essentially equivalent to that observed for the ternary complex inEscherichia coli. The binding of EF-Tumt to EF-Tsmt is mutually exclusive with the formation of the ternary complex. K Ts was determined by quantifying the effects of increasing concentrations of EF-Tsmt on the amount of ternary complex formed with EF-Tumt. The value obtained for K Ts(5.5 ± 1.3 nM) is comparable to the value ofK tRNA.


© 2000 American Society for Biochemistry and Molecular Biology Inc. Original published version available at

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Journal of Biological Chemistry



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Chemistry Commons



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