Studies on the interaction of elfamycin antibiotics with elongation factor-Tu by mass spectroscopic techniques

Elfamycin antibiotics have been studied by mass spectrometry, using direct-liquid-introduction chemical ionization and fast-atom bombardment (FAB), but these techniques are not suitable for the identification of the interaction product between antibiotic and elongation factor-Tu (EF-Tu). A new mass spectrometric technique, matrix-assisted laser desorption (MALD), has been employed to clearly identify the complex formed between EF-Tu and kirromycin. Using MALD operated in the positive-ion mode, molecular weight values of 43 330 and 44 234 Da were obtained for EF-Tu and the adduct EF-Tu/kirromycin, respectively; both are close to the theoretically calculated values of 43 225 and 44 060. These measurements suggest that MALD techniques can be used to obtain useful information on EF-Tu/elfamicyn antibiotic interaction. Other techniques, such as desorption chemical ionization, FAB and thermospray have been used to obtain information on the fragmen-tation patterns of some elfamycins (kirrotmycin, aurodox, efrotomycin). In particular, the positive-ion FAB spectrum of efrotomycin obtained by using a matrix of glycerol and water containing K+ ions, contained the quasimolecular ion [M + K]+ at m/z 1184. Thermospray appeared to be the best technique for structural elucidation studies. In fact, positive-ion spectra of kirromycin, aurodix and efrotomycin are characterized by significant fragmentation ions, while molecular ions are of very low intensity.