Purification of four penicillin-binding proteins from Bacillus megaterium.

Four of the five penicillin-binding proteins in the cytoplasmic membranes of Bacillus megaterium have been purified to protein homogeneity. The method used involved the solubilization of the penicillin-binding proteins from the membranes by treatment with non-ionic detergent, followed by partial separation of the proteins by ion-exchange chromatography on DEAE-Sepharose CL-6B. Each protein was then purified to protein homogeneity by covalent affinity chromatography on ampicillin-affinose. The protein with the lowest molecular weight is a DD-carboxypeptidase. The other three proteins have previously been postulated to be peptidoglycan transpeptidases, endopeptidases or DD-carboxypeptidases in vivo, but it was not possible to demonstrate any of these activities with the purified proteins in various in vitro systems. Possible reasons for the observed lack of enzymic activity in vitro are discussed.