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351.
Defective biliary secretion of bile acid 3-O-glucuronides in rats with hereditary conjugated hyperbilirubinemia 总被引:1,自引:0,他引:1
F Kuipers A Radominska P Zimniak J M Little R Havinga R J Vonk R Lester 《Journal of lipid research》1989,30(12):1835-1845
Biliary secretion of bile acid glucuronides was studied in control rats and in rats with a congenital defect in hepatobiliary transport of organic anions (GY rats). In control animals, hepatobiliary transport of [3H]lithocholic acid 3-O-glucuronide and [3H]cholic acid 3-O-glucuronide was efficient (greater than 95% in 1 h) and comparable to that of [14C]taurocholic acid. Secretion of both glucuronides was impaired in GY rats (24% and 71% at 1 h), whereas that of taurocholate was similar to control values. However, recovery of the glucuronides in bile was nearly complete within 24 h; virtually no radioactivity was found in urine. In control rats, biliary secretion of lithocholic acid 3-O-glucuronide, but not that of cholic acid 3-O-glucuronide or taurocholate, could be delayed by simultaneous infusion of dibromosulphthalein. In mutant rats, dibromosulphthalein infusion was also able to inhibit secretion of cholic acid 3-O-glucuronide. [3H]Hydroxyetianic acid, a C20 short-chain bile acid, was secreted by control rats as a mixture of 20% carboxyl-linked and 80% hydroxyl-linked (3-O-)glucuronide; secretion was very efficient (99% in 1 h). In GY rats, secretion was drastically impaired (16% at 1 h and 74% over a 24-h period). Initially, the mutant secreted more carboxyl- than hydroxyl-linked glucuronide, but the ratio reached that of control animals after 24 h. The rates of formation of both types of hydroxyetianic acid glucuronide by hepatic microsomes from mutant rats were similar or even slightly higher than those of control microsomes. These findings indicate that bile acid 3-O-glucuronides, but probably not carboxyl-linked glucuronides, are secreted into bile by a transport system shared with organic anions such as conjugated bilirubin and dibromosulphthalein, but different from that for amino acid-conjugated bile acids. 相似文献
352.
353.
Adam R Burns W Zac Stephens Keaton Stagaman Sandi Wong John F Rawls Karen Guillemin Brendan JM Bohannan 《The ISME journal》2016,10(3):655-664
Despite their importance to host health and development, the communities of microorganisms associated with humans and other animals are characterized by a large degree of unexplained variation across individual hosts. The processes that drive such inter-individual variation are not well understood. To address this, we surveyed the microbial communities associated with the intestine of the zebrafish, Danio rerio, over developmental time. We compared our observations of community composition and distribution across hosts with that predicted by a neutral assembly model, which assumes that community assembly is driven solely by chance and dispersal. We found that as hosts develop from larvae to adults, the fit of the model to observed microbial distributions decreases, suggesting that the relative importance of non-neutral processes, such as microbe-microbe interactions, active dispersal, or selection by the host, increases as hosts mature. We also observed that taxa which depart in their distributions from the neutral prediction form ecologically distinct sub-groups, which are phylogenetically clustered with respect to the full metacommunity. These results demonstrate that neutral processes are sufficient to generate substantial variation in microbiota composition across individual hosts, and suggest that potentially unique or important taxa may be identified by their divergence from neutral distributions. 相似文献
354.
We sampled populations of forest-floor dwelling cave and ground wētā using footprint tracking tunnels and spotlight transect counts in southern beech forest, New Zealand. Samples were compared to estimates of wētā density based on mark–recapture estimates from 25?m2 enclosures. Both activity indices captured variability in cave wētā in time and space, were strongly correlated with each other, and have the potential for monitoring cave wētā activity levels. Comparisons between indices and cave wētā density estimates were equivocal, as recapture rates were too low to calculate high-resolution density estimates. We also found that cave wētā counts had a curved relationship increasing with temperature, and a negative relationship with increasing shrub and woody debris cover. Based on these preliminary results, tracking tunnels could be a viable method of monitoring cave wētā as they appear more efficient than transect counts and are relatively inexpensive. However, further calibration trials are needed to determine if indices mirror robust population density estimates. 相似文献
355.
356.
Heterologous expression of an engineered truncated form of human Lewis fucosyltransferase (Fuc-TIII) by the methylotrophic yeast Pichia pastoris 总被引:1,自引:0,他引:1
Gallet PF; Vaujour H; Petit JM; Maftah A; Oulmouden A; Oriol R; Le Narvor C; Guilloton M; Julien R 《Glycobiology》1998,8(9):919-925
A stable GS115 Pichia pastoris recombinant strain was constructed to
secrete a truncated form of the human alpha(1,3/4) fucosyltransferase
(amino acids 45-361). Enzyme production resulted from a secretory pathway
based on the pre-pro- alpha mating factor signal sequence of the yeast
Saccharomyces cerevisiae . Following its transit through the Golgi
apparatus, the enzyme accumulated in the periplasmic space before its
release in the culture broth (about 30 mg/l). Cell-enclosed enzyme (
approximately 0.16%) proved to be fairly stable for many freezing and
thawing cycles and could be used several times as an immobilized catalyst.
Soluble enzyme (>99.8%) representing the main protein of the culture
broth (10%) has been characterized by Western-blotting, substrate
specificities and kinetic parameters. The two forms (cell- enclosed and
soluble) of recombinant enzyme may be used for in vitro synthesis of
Lewisadeterminants.
相似文献
357.
Size homoplasy and mutational processes of interrupted microsatellites in two bee species, Apis mellifera and Bombus terrestris (Apidae) 总被引:6,自引:0,他引:6
Similar microsatellite electromorphs (PCR products of the same size) can
arise from independent mutational events. Such alleles are not identical by
descent. This phenomenon, termed size homoplasy, was studied by sequencing
electromorphs of two microsatellite loci in which the stretch of basic
repeats is interrupted by different short (1-2 bp) DNA motifs. The number
and position of these interruptions were established for electromorphs from
closely and distantly related populations of honeybees and bumblebees. No
sequence difference was found when electromorphs came from the same
subspecies or from closely related subspecies, suggesting that they were
probably identical by descent. In contrast, sequence differences were often
detected in distantly related subspecies, showing that size homoplasy
frequently occurs at this level of population differentiation. Size
homoplasy is increased by limits to free length variation of alleles, a
phenomenon that seems to act on interrupted microsatellites when comparing
distantly related taxa, that is, honeybee subspecies from different
evolutionary lineages. Electromorph sequences suggest that, within the
scope of these limits, large mutation events have occurred frequently at
both interrupted loci studied. In good agreement with the molecular data,
computations based on the observed heterozygosity and number of
electromorphs and simulation studies showed that neither locus fits the
one-step stepwise mutant model (SMM). We speculate that interrupted
microsatellites in general could be characterized by a higher variance in
repeat number and consequently a lower homoplasy rate than pure ones.
Hence, interrupted microsatellites should be most appropriate for
investigating population differentiation and evolutionary relationship
between relatively distant populations.
相似文献
358.
359.
The fungitoxicity of mercuric chloride to Aspergillus niger was increased in the presence of d-, l-, dl-methionine, dl-ethionine, dl-S-methylcysteine or sodium methylmercaptide. The same effect was observed with methionine for two other fungi investigated: Cladosporium cucumerinum and Scopulariopsis brevicaulis. It is suggested that this effect can be ascribed to the formation of CH3SHg+ or (CH3S)2Hg, or the corresponding ethyl compounds. CH3SHgCl and (CH3S)2Hg were synthetically prepared and proved indeed far more fungitoxic than HgCl2. The hypothesis was further substantiated by the observation that A. niger rapidly converts dl-methionine into CH3SH, which undoubtedly reacts with Hg2+ to give the above mentioned methylthiomercury compounds. 相似文献
360.