Differential permeability for lipophilic compounds in uncoupler-resistant cells of Escherichia coli

Subsequent products after antioxidant actions of beta-carotene and alpha-tocopherol have no Salmonella mutagenicity

Beta-carotene and alpha-tocopherol are important antioxidants biologically, but whether their oxidized products are toxic or not remains to be discovered. Here, we chromatographically separated 5 pure products or isomeric mixtures from reaction mixtures of beta-carotene and reactive oxygens, and 17 lipid-radical scavenging products of alpha-tocopherol. The products were tested for mutagenicity using Salmonella typhimurium TA98, TA100, TA102, and TA104, in the presence and absence of S9. None showed mutagenicity against any of the four strains, or cytotoxicity that influenced the survival of the bacteria. Lipid-peroxides have been known to increase the formation of mutagens from dietary procarcinogens such as heterocyclic amines. So, we also measured the activity to increase 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2) mutagenicity. The products from beta-carotene and alpha-tocopherol did not increase, but rather several of them suppressed, the mutagenicity of Trp-P-2. Thus, the products of beta-carotene and alpha-tocopherol formed after the antioxidant actions were not genotoxic.

Bacterial resistance to uncouplers

Uncoupler resistance presents a potential challenge to the conventional chemiosmotic coupling mechanism. In E. coli, an adaptive response to uncouplers was found in cell growing under conditions requiring oxidative phosphorylation. It is suggested that uncoupler-resistant mutants described in the earlier literature might represent a constitutive state of expression of this "low energy shock" adaptive response. In the environment, bacteria are confronted by nonclassical uncoupling factors such as organic solvents, heat, and extremes of pH. It is suggested that the low energy shock response will aid the cell in coping with the effects of natural uncoupling factors. The genetic analysis of uncoupler resistance has only recently began, and is yielding interesting and largely unexpected results. In Bacillus subtilis, a mutation in fatty acid desaturase causes an increased content of saturated fatty acids in the membrane and increased uncoupler resistance. The protonophoric efficiency of uncouplers remains unchanged in the mutants, inviting nonorthodox interpretations of the mechanism of resistance. In E. coli, two loci conferring resistance to CCCP and TSA were cloned and were found to encode multidrug resistance pumps. Resistance to one of the uncouplers, TTFB, remained unchanged in strains mutated for the MDRs, suggesting a resistance mechanism different from uncoupler extrusion.

Isolation of Tn917 insertional mutants of Bacillus subtilis that are resistant to the protonophore carbonyl cyanide m-chlorophenylhydrazone

Tn917 transposition libraries prepared from Bacillus subtilis were screened for mutants that had insertions in the chromosome resulting in resistance to the protonophore carbonylcyanide m-chlorophenylhydrazone (CCCP). Five such strains were characterized. Three of these were found to have distinct insertion sites that resulted in changes in fatty acid composition of the membrane lipids. The lipid changes were qualitatively similar to changes observed earlier in CCCP-resistant strains of B. subtilis that had been isolated after chemical mutagenesis. However, the extent of the changes was more modest, correlating with a lower level of protonophore-resistance. One of these mutants was disrupted in a gene homologous to the Escherichia coli rho gene, as reported earlier (Quirk et al. (1993) J. Bacteriol. 175, 647-654), one was disrupted in a new member of the two-component signalling systems, and the third was disrupted in a new gene of unknown function that apparently forms an operon with transporter genes. The other two CCCP-resistant mutants were disrupted in genes that are likely to encode membrane transporters; the disruption of these genes may have reduced the transmembrane ion leaks during growth, thus conferring modest protonophore-resistance. In one of these strains, the disrupted gene is part of an apparent operon that is a homologue of iron uptake operons from other prokaryotes.

Mechanism of uptake of the fluorescent dye 2-(4-dimethylaminostyryl)-1-ethylpyridinium cation (DMP+) by phospholipid vesicles

The fluorescent dye 2-(4-dimethylaminostyryl)-1-ethylpyridinium cation (DMP+) is taken up by liposomes of egg phosphatidylcholine in response to the imposition of a transmembrane potential. Entry of DMP+ into the bilayer driven by the transmembrane potential is accompanied by a change in the fluorescence emission maximum of the dye. This change reflects the movement of the dye molecules from the headgroup region of the bilayer into the region of the fatty acyl chains. It is released into the external aqueous phase on discharge of the transmembrane potential. Partition of the dye into the phospholipid bilayer is favoured by the presence of negatively charged lipids, such as dioleoylphosphatidic acid and dicetyl phosphate, in the bilayer. Stearylamine opposes entry of the dye into the bilayer. Tetraphenylboron (TPB-) increases the partitioning of DMP+ into the phospholipid bilayer even in the absence of a transmembrane potential. The fluorescence emission maximum of DMP+ under these conditions is similar to that observed in the absence of TPB- following imposition of the transmembrane potential. It is suggested that TPB- facilitates the entry of DMP+ into the fatty acyl chain regions of the phospholipid bilayer.