Physiological suppression of a transport defect in Escherichia coli mutants deficient in Ca²⁺, Mg²⁺ stimulated adenosine triphosphatase

Transport properties of membrane vesicles isolated from two adenosine triphosphatase deficient mutants of E. coli, NR70 and DL54, were compared with those of vesicles prepared from the corresponding parental strains. As reported previously, vesicles prepared from these mutants grown under aerobic conditions exhibited defective amino acid transport, and activity was restored after treatment with dicyclohexylcarbodiimide. In sharp contrast, however, vesicles isolated from the same mutants grown anaerobically in the presence of nitrate exhibited completely normal transport activity when assayed under either anaerobic or aerobic conditions. Suppression of the transport defect was not due to the manner by which the vesicles were prepared, and the adenosine triphosphatase deficiency was not ameliorated by anaerobic growth in the presence of nitrite. Finally, the transport activity of vesicles prepared from the mutants grown under aerobic conditions was relatively resistant to the effect of 1.0 M guanidine hydrochloride extraction, whereas the activity of vesicles prepared from mutants grown anaerobically was totally refractory to the effect of the chaotrope.