The roles of the polytopic membrane proteins NarK, NarU and NirC in Escherichia coli K-12: two nitrate and three nitrite transporters bic product of the third gene of the nir operon, which is predicted to be a polytopic membrane protein with six membrane-spanning helices. Deletion of both NarK and NirC decreased nitrite uptake and reduction to a basal rate that was fully restored by a single chromosomal copy of either narK or nirC. A multicopy plasmid encoding NarU complemented a narK mutation for nitrite excretion, but not for nitrite uptake. We conclude that, in contrast to NirC, which transports only nitrite, NarK and NarU provide alternative mechanisms for both nitrate and nitrite transport. However, NarU might selectively promote nitrite excretion, not nitrite uptake.

Cross-talk between TGF-beta and IL-6 has been shown to direct the differentiation of CD4(+) cells into special IL-17-secreting cells, which are termed Th17 cells. In this study, we demonstrated that TGF-beta and IL-6 could stimulate CD8(+) cells to differentiate into noncytotoxic, IL-17-producing cells in MLC. These IL-17-producing CD8(+) cells exhibit a unique granzyme B(-)IFN-gamma(-)IL-10(-) phenotype. The mRNA level of Th2/T cytotoxic 2 (Tc2) transcription factors GATA3 and Th1/Tc1 transcription factors T-box expressed in T cell (T-bet) as well as its target H2.O-like homeobox (Hlx) is decreased in CD8(+) cells from TGF-beta- and IL-6-treated MLC. In addition, these CD8(+) cells display a marked up-regulation of retinoic acid-related orphan receptor-gammat, a key IL-17 transcription factor. These results demonstrate that the existence of an IL-17-producing CD8(+) subset belongs to neither the Tc1 nor the Tc2 subset and can be categorized as a T noncytotoxic 17 (Tnc17) subset.

Gastrointestinal (GI) tract leucine metabolism was measured in 6- to 9-mo-old lambs subjected to trickle infection with Trichostrongylus colubriformis larvae and in separate animals that were not infected. Animals prepared with a jejunal catheter and with indwelling catheters into the aorta and the portal- (PDV) and mesenteric- (MDV) drained viscera were infused simultaneously with [1-13C] and [5,5,5-2H3] leucine to determine GI tract sequestration of leucine from arterial and luminal amino acid pools by tracer and tracee arteriovenous concentration differences. Leucine oxidative losses and net fluxes were also determined across the GI tract. Infection had no detectable effect on whole-body leucine flux, but it increased total GI tract leucine sequestration by 24% (P<.05) and GI tract oxidative losses of leucine by 22 to 41% (P<.01). Net PDV fluxes of leucine were decreased by 20 to 32% during the infection. The infection did not alter either the proportion of precursor leucine used by GI tract metabolism that was derived from the arterial leucine pool (.84 to .88) or the proportional sequestration of digesta-derived leucine during "first pass" absorptive metabolism (.12 to .18). These findings help to elucidate the metabolic basis for the reduced growth rates and nitrogen retention observed when animals are subjected to subclinical nematode infection.

Two SDS-resistant endochitinases, designated as ASCHI53 and ASCHI61, were isolated from Aeromonas schubertii in a soil sample from southern Taiwan. MALDI-TOF mass measurement indicates the molecular weights of 53,527 for ASCHI53 and 61,202 for ASCHI61. N-terminal and internal amino acid sequences were obtained, and BLAST analysis of the sequences and MS/MS peptide sequencing showed that they were novel proteins. Degradation of chitin by these two endochitinases gave rise to hexameric chitin oligosaccharide, a compound known to have several potent biomedical functions. ASCHI53 and ASCHI61 retained, respectively, 65% and 75%, of their chitinase activity in the presence of 5% SDS and 100% of their activity in the presence of 10% b-mercaptoethanol. These results demonstrate that they are SDS-resistant endochitinases and probably have a rigid structure. V

Members of genus Xenorhabdus are symbiotically associated with entomopathogenic nematodes of genus Steinernema. Herein, we describe the isolation and purification of four novel metabolites, xenocyloins G-J (1-4), from liquid cultures of Xenorhabdus bovienii SN52 by extensive column chromatography and semi-preparative HPLC. Chemical structures of the xenocyloin derivatives were determined based on comprehensive NMR spectra and HR-ESI-MS analyses. All compounds exhibited significant collagen-induced anti-platelet aggregation activities, among which xenocyloin H (2) exhibited the strongest activity with an inhibition rate of 96.0 ± 0.1% at a concentration of 50 μM. The xenocyloin G (1) and H (2) exhibited anti-platelet activities with IC 50 values which were 31.7 ± 4.4 μM and 27.5 ± 3.5 μM respectively; whilst under similar conditions the IC 50 value for aspirin was 289.5 ± 15.7 μM, nearly ten times less than 1 and 2.