EFFECT OF pH AND AMMONIUM IONS ON THE PERMEABILITY OFBACILLUS PASTEURII

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Abstract
Wiley, W. R. (Washington State University, Pullman),and J. L. Stokes. Effect of pH and ammonium ions on the permeability ofBacillus pasteurii. J. Bacteriol.86:1152–1156. 1963.—Cell suspensions ofBacillus pasteuriirequire an alkaline pH (8.5 to 9.0) and NH4+for the oxidation of low concentrations (4 μm) of fumaric acid, glutamic acid, alanine, and other oxidizable substrates. In contrast, cells disrupted by a French press or by lysozyme oxidize these substrates at pH 7.2 and without NH4+. Moreover, the alkaline pH and NH4+inhibit substrate oxidation by the broken cells. These striking differences between whole and disrupted cells suggest that pH and NH4+affect whole cells externally and not internally. It appears that the alkaline pH is needed to convert NH4+to free NH3. The latter in turn is required by the cells for the transport of low concentrations of substrate across the cell membrane. At high concentrations (20 to 250 μm), substrates force entry into the cells by simple diffusion, thereby eliminating the need for a high pH and NH4+for oxidation.