Binding of14C-penicillin G toProteus mirabilis

Summary The binding of radioactivity from¹⁴C-penicillin G labelled in the acyl side chain toProteus mirabilis D 52 was examined.Under the conditions of the binding assay about 90% of the cells lost their viability upon saturation with radioactivity from¹⁴C-penicillin G which required 18 g penicillin G/mg dry weight of cells and an incubation time of 2 h at 37° C.Examination of 6-aminopenicillanic acid showed that this compound, in contrast to grampositive bacteria, has little effect on the binding of radioactivity from¹⁴C-penicillin G toP. mirabilis D 52. In contrast to 6-aminopenicillanic acid, inhibition of binding of radioactivity from¹⁴C-penicillin G toP. mirabilis D 52 is obtained with phenacetylglycine, a compound considered as structural analogue of the acyl side chain in penicillin G. In addition, this compound interferes with a basic property of penicillin G in that in its presence formation of sphaeroplasts is prevented. A reaction, specific for gramnegative bacteria, is proposed in which the acyl side chain of penicillin G is transfered to a cellular component.