Inactivation of beta-lactamase from Shigella flexneri UCSF-129 by 6-beta-iodopenicillanic acid: classification of the enzyme.

The beta-lactamase from Shigella flexneri UCSF-129 was irreversible inactivated by 6-beta-iodopenicillanic acid. Only one serine residue was modified, according to the spectra change and the amino acid analyses. A pH variation of 0.3 units was found when the chemically modified enzyme was submitted to isoelectric focusing. The inactivation constant of the fast time course reaction was 0.1 seg-1. Protection of 96% was obtained, using cephradine 2,830 times more concentrated than 6-beta-iodopenicillanic acid. It is suggested that this enzyme belongs to class A, according to Ambler (1980).