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.