Salmonella typhimurium contains an anion-selective outer membrane porin induced by phosphate starvation.

A mutant of Salmonella typhimurium was selected that is constitutive for the pho regulon. It exhibited constitutive glycerol-3-phosphate transport activity and synthesized a new outer membrane porin. Upon measurement of porin activity in black lipid films, it exhibited anion selectivity. It therefore appears analogous to the Escherichia coli PhoE porin.     

Maltose-binding protein does not modulate the activity of maltoporin as a general porin in Escherichia coli.

Maltoporin (lambda receptor) is part of the maltose transport system in Escherichia coli and is necessary for the facilitated diffusion of maltose and maltodextrins across the outer membrane. Maltoporin also allows the diffusion of nonmaltodextrin substrates, albeit with less efficiency. The preference of maltoporin for maltodextrins in vivo is thought to be the result of an interaction of maltoporin with the maltose-binding protein, the malE gene product. In a recent report Heuzenroeder and Reeves (J. Bacteriol. 144:431-435, 1980) suggested that this interaction establishes a gating mechanism which inhibits the diffusion of nonmaltodextrin substrates, such as lactose. To reinvestigate this important conclusion, we constructed ompR malTc strains carrying either the malE+ gene, the nonpolar malE444 deletion, or the malE254 allele, which specifies an interaction-deficient maltose-binding protein. Lactose uptake was measured at different concentrations below the Km of this transport system and under conditions where transport was limited by the diffusion through maltoporin. We found no difference in the kinetics of lactose uptake irrespective of the malE allele. We conclude that the maltose-binding protein does not modulate the activity of maltoporin as a general outer membrane porin.     

The mglB sequence of Salmonella typhimurium LT2; promoter analysis by gene fusions and evidence for a divergently oriented gene coding for the mgl repressor

Summary The mglB gene of Salmonella typhimurium LT2 coding for the galactose-binding protein (GBP) was sequenced. We compared the deduced amino acid sequence with the GBP sequence of Escherichia coli K12. The mature proteins differ in only 19 of 309 amino acid residues, corresponding to 94% homology. Analysis of the mglB control region by promoter-probe vectors revealed that two promoters, P1 and P2, constitute the mgl control region (P _mgl ). P1 and P2 function in a synergistic way. P1 is the main promoter of the operon; its activity is 20 times the activity of P2. Both promoters are activated by the cyclic adenosine monophosphate catabolite activator protein (cAMP/CAP) complex. While P1 is inactive in the absence of the cAMP/CAP complex, there is residual activity of P2 under these conditions. Studies on the inducibility of the mglBAEC operon using multicopy plasmid promoter-probe vectors were hampered by the titration of the mgl repressor resulting in a partially constitutive expression of the mgl operon. The results indicate that only P1 is responding to induction by D-fucose. A weak promoter, P _D , within the P1 region but divergent to it was found. P _D is neither stimulated by the cAMP/CAP complex nor by D-fucose. We cloned the gene located downstream to P _D and found it to strongly repress the expression of the mgl operon. We termed this gene mglD. The presence of D-fucose abolished the repression caused by the plasmid-encoded mglD gene product.Abbreviations IPTG isopropyl-1-thic--D-galatopyranoside - ONPG 2-nitrophenyl--D-galatopyranoside - XG 5-bromo-4-chloro-3-indolyl--D-galatopyranoside - Kan^r Kanamycin resistance     

High-affinity maltose/trehalose transport system in the hyperthermophilic archaeon Thermococcus litoralis.

The hyperthermophilic marine archaeon Thermococcus litoralis exhibits high-affinity transport activity for maltose and trehalose at 85 degrees C. The K(m) for maltose transport was 22 nM, and that for trehalose was 17 nM. In cells that had been grown on peptone plus yeast extract, the Vmax for maltose uptake ranged from 3.2 to 7.5 nmol/min/mg of protein in different cell cultures. Cells grown in peptone without yeast extract did not show significant maltose or trehalose uptake. We found that the compound in yeast extract responsible for the induction of the maltose and trehalose transport system was trehalose. [14C]maltose uptake at 100 nM was not significantly inhibited by glucose, sucrose, or maltotriose at a 100 microM concentration but was completely inhibited by trehalose and maltose. The inhibitor constant, Ki, of trehalose for inhibiting maltose uptake was 21 nM. In contrast, the ability of maltose to inhibit the uptake of trehalose was not equally strong. With 20 nM [14C]trehalose as the substrate, a 10-fold excess of maltose was necessary to inhibit uptake to 50%. However, full inhibition was observed at 2 microM maltose. The detergent-solubilized membranes of trehalose-induced cells contained a high-affinity binding protein for maltose and trehalose, with an M(r) of 48,000, that exhibited the same substrate specificity as the transport system found in whole cells. We conclude that maltose and trehalose are transported by the same high-affinity membrane-associated system. This represents the first report on sugar transport in any hyperthermophilic archaeon.     

Simultaneous determination of all-trans-, 13-cis- and 9-cis-retinoic acid, their 4-oxo metabolites and all-trans-retinol in human plasma by high-performance liquid chromatography

All-trans-retinoic acid (all-trans-RA) and 13-cis-retinoic acid (13-cis-RA), due to their effects on cell differentiation, proliferation and angiogenesis, improved treatment results in some malignancies. Pharmacokinetic studies of all-trans-RA and 13-cis-RA along with monitoring of retinoic acid metabolites may help to optimize retinoic acid therapy and to develop new effective strategies for the use of retinoic acids in cancer treatment. Therefore, we developed a HPLC method for the simultaneous determination in human plasma of the physiologically important retinoic acid isomers, all-trans-, 13-cis- and 9-cis-retinoic acid, their 4-oxo metabolites, 13-cis-4-oxoretinoic acid (13-cis-4-oxo-RA) and all-trans-4-oxoretinoic acid (all-trans-4-oxo-RA), and vitamin A (all-trans-retinol). Analysis performed on a silica gel column with UV detection at 350 nm using a binary multistep gradient composed on n-hexane, 2-propanolol and glacial acetic acid. For liquid-liquid extraction a mixture of n-hexane, dichloromethane and 2-propanolol was used. The limits of detection were 0.5 ng/ml for retinoic acids and 10 ng/ml for all-trans-retinol. The method showed good reproducibility for all components (within-day C.V.: 3.02–11.70%; day-to-day C.V.: 0.01–11.34%. Furthermore, 9-cis-4-oxoretinoic acid (9-cis-4-oxo-RA) is separated from all-trans-4-oxo-RA and 13-cis-4-oxo-RA. In case of clinical use of 9-cis-retinoic acid (9-cis-RA) the pharmacokinetics and metabolism of this retinoic acid isomer can also be examined.     

Population density of the Réunion Grey White-eye Zosterops borbonicus within the summit ecosystems of Réunion,Mascarene Islands

Assessing population density is crucial for studying the ecology and evolutionary biology of species as well as for conservation purposes. Here we used point count methods to infer population density in a single-island endemic passerine bird, the Réunion Grey White-eye Zosterops borbonicus, that displays striking evidence of differentiation at a small spatial scale. Population density was estimated at 5.17 birds ha^?1 (CL 4.85–5.50), a value somewhat higher than previously believed. This estimation provides the first detailed estimation of bird population density in the vulnerable summit ecosystems of Réunion and will possibly allow a better understanding of the evolutionary causes of this plumage colour variation.