Journal of Antimicrobial Chemotherapy (1999) 44, 593-599
© 1999 The British Society for Antimicrobial Chemotherapy
Interactions of 
- and ß-avoparcin with bacterial cell-wall receptor-mimicking peptides studied by electrospray ionization mass spectrometry
Department of Biomolecular Mass Spectrometry Bijvoet, Center for Biomolecular Research, Department of Chemistry and Department of Pharmacy, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands
Solution phase affinity constants of the glycopeptide antibiotic 
- and
ß-avoparcin, with a range of bacterial cell-wall receptor-mimicking model peptides, were
determined by a relatively new method: affinity electrospray ionization mass spectrometry
(ESI-MS). This method is relatively efficient and allows the parallel determination of several
affinity constants in mixtures of antibiotics and receptors. The determined binding constants for
- and ß-avoparcin were compared with those of the related glycopeptide antibiotic
vancomycin. The solution phase binding affinities of - and ß-avoparcin on one hand,
and vancomycin on the other, were found to be in the same order, at least for the range of
receptor-mimicking peptides studied. However, ß-avoparcin displayed slightly higher
binding affinities than -avoparcin, particularly for strong binding receptor-mimicking
peptides. The evidence that - and ß-avoparcin and vancomycin are structurally similar,
combined with the present data revealing their similar affinity for bacterial cell-wall
receptor-mimicking peptides, supports the hypothesis that the appearance of
vancomycin-resistant enterococci (VRE) might be linked to the widespread use of avoparcin.
* Corresponding author. Fax: +31-30-251-8219; E-mail: a.j.r.heck{at}chem.uu.ul