Cross-links in cell walls of Bacillus subtilis by rotational-echo double-resonance 15N NMR.

The cross-link index of peptidoglycan of intact cell walls of Bacillus subtilis grown in media containing L-[2-13C,15N]aspartic acid has been determined by rotational-echo double-resonance 15N NMR. A cross-link index of 72% decreased to 47% when the bacteria were exposed to the antibiotic cephalosporin C. The fraction of 15N label routed from aspartic acid in the media to glutamic acid in the peptidoglycan peptide stems more than doubled for the cephalosporin-exposed cells, indicating interference with general cell wall nitrogen metabolism by the antibiotic.