The cell density-dependent acid sensitivity phenotypes of Escherichia coli strains K-12 and O157:H7 were examined with reference to three possible mechanisms of acid resistance. There was no evidence of any diffusible substance released from dead cells which could influence the cell density-dependent acid survival phenotype. Instead, cell density-dependent acid survival phenotype was associated...

1. The subcellular distributions of glutamate decarboxylase and aspartate transaminase were studied in rat and guinea-pig brain. 2. Glutamate decarboxylase is localized in the synaptosome fraction. The mean density of the particles containing the enzyme is slightly greater than those derived from cholinergic neurones, though overlap is substantial. 3. The enzyme is readily released from synapto...