The Antibiotics Kirromycin and Pulvomycin Bind to Different Sites on the Elongation Factor Tu from Esclzerichia coli

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Abstract
Pulvomycin and kirromycin, two antibiotics which inhibit protein biosynthesis in Escherichiu coli by complex formation with the elongation factor Tu (EF‐Tu), bind to different sites on the protein. While only one molecule of kirromycin can be bound to one molecule of EF‐Tu, more than one molecule of pulvomycin interacts with a molecule of EF‐Tu. This has been deduced from experiments in which the aminoacyl‐tRNA binding and the GTPase activity of EF‐Tu were measured in the presence of varying amounts of both antibiotics. These experi‐ ments are interpreted to mean that pulvomycin but not kirromycin can replace the other antibiotic in its respective site. Our conclusions are supported by circular dichroism spectroscopy.