Kirromycin

Kirromycin (Mocimycin; Delvomycin) is an elongation factor Tu (EF-Tu) inhibitor targeting protein biosynthesis. As an antibiotic, Kirromycin exerts antibacterial activity against Gram-negative bacteria by acting on EF-Tu to interfere with the peptidyl transfer reaction. Kirromycin is applicable to studies on bacterial infections^[1][2][3]. In Vitro:Kirromycin (5 min) potently inhibits poly (U)-directed polyphenylalanine synthesis in an *E. coli* cell-free translation system, with an IC₅₀ of 5 × 10^-7 M^[1].
Kirromycin (5 min) doubles the EF-T-dependent GTP hydrolysis activity, strongly inhibits EF-T-dependent peptide bond formation, and does not alter EF-T-mediated binding of Phe-tRNA^Phe to ribosomes in the *Escherichia coli* ribosome assay system^[1].
When incubated with EF-T and GTP for 5 min, kirromycin increases the binding amount of [³H]GTP to *Escherichia coli* EF-T to more than three times the original level^[1].
Kirromycin (500 pmol; 10 min) induces Escherichia coli EF-T-dependent GTP hydrolysis in the absence of ribosomes or aminoacyl-tRNA; this activity is specifically activated only in the presence of Phe-tRNA^Phe (but not uncharged tRNA^Phe or Ac-Phe-tRNA^Phe); it significantly enhances this activity in the presence of ribosomes; its GTP K_m is 2 × 10^-7 M, which is consistent with the GTP K_m of ribosome- and Phe-tRNA^Phe-dependent EF-T GTPase in the absence of antibiotics^[1].
Kirromycin (1 nmol; 5 min) enables EF-T-dependent binding of Phe-tRNA^Phe to poly (U)-ribosome complexes in *E. coli* in the absence of GTP, with the amount of [¹⁴C]Phe-tRNA^Phe bound to ribosomes reaching 3.5 pmol^[1].
At 4°C, kirromycin reduces the affinity of *E. coli* EF-Tu-GTP for aa-tRNA by approximately 3 orders of magnitude, resulting in a K_d of 2 μM; it also equalizes the affinity of *E. coli* EF-Tu-GDP for aa-tRNA to a K_d of 7 μM at 4°C, thereby eliminating the significant difference in affinity between EF-Tu-GTP and EF-Tu-GDP for aa-tRNA observed in the absence of this antibiotic^[3].
Kirromycin (0.4-26 μM) binds to EF-Tu-GDP (as well as EF-Tu-GTP) from *E. coli* at a 1:1 molar ratio to form a complex, induces conformational changes that increase the net negative charge and electrophoretic mobility of EF-Tu, and exhibits an extremely low dissociation rate^[3].