Direct measurement of peptidoglycan cross-linking in bacteria by 15N nuclear magnetic resonance.

Cross-polarization magic angle spinning 9.12-MHz 15N nuclear magnetic resonance was used to measure the extent of peptidoglycan cross-linking within intact bacterial cells and isolated cell walls of Aerococcus viridans ATCC 10400 grown in the presence of L-[epsilon-15N]lysine. A value of 49% for the cross-linking index was found for normal cells, while for those grown in the presence of low levels of penicillin G (0.1 micrograms/ml), the cross-linking index was reduced to 35%.