Micelle formation of sodium chenodeoxycholate and solubilization into the micelles: comparison with other unconjugated bile salts

Micellization of sodium chenodeoxycholate (NaCDC) was studied for the critical micelle concentration (CMC), the micelle aggregation number, and the degree of counterion binding to micelle at 288.2, 298.2, 308.2, and 318.2 K. They were compared with those of three other unconjugated bile salts; sodium cholate (NaC), sodium deoxycholate (NaDC), and sodium ursodeoxycholate (NaUDC). The I(1)/I(3) ratio of pyrene fluorescence and the solubility dependence of solution pH were employed to determine the CMC values. As the results, a certain concentration range for the CMC and a stepwise molecular aggregation for micellization were found reasonable. Using a stepwise association model of the bile salt anions, the mean aggregation number (n) of NaCDC micelles was found to increase with the total anion concentration, while the n values decreased with increasing temperature; 9.1, 8.1, 7.4, and 6.3 at 288.2, 298.2, 308.2, and 318.2 K, respectively, at 50 mmol dm(-3). The results from four unconjugated bile salts indicate that the number, location, and orientation of hydroxyl groups in the steroid nucleus are quite important for growth of the micelles. Activity of the counterion (Na(+)) was determined by a sodium ion selective electrode in order to confirm the low counterion binding to micelles. The solubilized amount of cholesterol into the aqueous bile salt solutions increased in the order of NaUDC相似文献   

Role of 57-72 loop in the allosteric action of bile salts on pancreatic IB phospholipase A2: Regulation of fat and cholesterol homeostasis

Mono- and biphasic kinetic effects of bile salts on the pancreatic IB phospholipase A2 (PLA2) catalyzed interfacial hydrolysis are characterized. This novel phenomenon is modeled as allosteric action of bile salts with PLA2 at the interface. The results and controls also show that these kinetic effects are not due to surface dilution or solubilization or disruption of the bilayer interface where in the mixed-micelles substrate replenishment becomes the rate-limiting step. The PLA2-catalyzed rate of hydrolysis of zwitterionic dimyristoylphosphatidylcholine (DMPC) vesicles depends on the concentration and structure of the bile salt. The sigmoidal rate increase with cholate saturates at 0.06 mole fraction and changes little at the higher mole fractions. Also, with the rate-lowering bile salts (B), such as taurochenodeoxycholate (TCDOC), the initial sigmoidal rate increase at lower mole fraction is followed by nearly complete reversal to the rate at the pre-activation level at higher mole fractions. The rate-lowering effect of TCDOC is not observed with the (62-66)-loop deleted ΔPLA2, or with the Naja venom PLA2 that is evolutionarily devoid of the loop. The rate increase is modeled with the assumption that the binding of PLA2 to DMPC interface is cooperatively promoted by bile salt followed by allosteric k_cat^?-activation of the bound enzyme by the anionic interface. The rate-lowering effect of bile salts is attributed to the formation of a specific catalytically inert E^?B complex in the interface, which is noticeably different than the 1:1 EB complex in the aqueous phase. The cholate-activated rate of hydrolysis is lowered by hypolidemic ezetimibe and guggul extract which are not interfacial competitive inhibitors of PLA2. We propose that the biphasic modulation of the pancreatic PLA2 activity by bile salts regulates gastrointestinal fat metabolism and cholesterol homeostasis.     

Mandibular gland secretions of workers of Myrmica rugulosa and M.schencki: comparison with four other Myrmica species

ABSTRACT. The mandibular glands of the two species of ant, Myrmica schencki Em. and Myrmica rugulosa Nyl., contain mixtures of similar compounds, but in different proportions. M.rugulosa produces 3-pentanol, 3-hexanone, 3-hexanol, 3-heptanone, 3-heptanol, 3-octanone (by far the most abundant component), 3-octanol, 3-nonanol, 3-decanone and 6-methyl-3-octanone, in addition to small amounts of ethanal, acetone and methylpropanal. M.schencki produces most of these (though much less 3-octanone and much more 3-octanol), but also produces significant amounts of 3-nonanol, 3-decanol and 6-methyl-3-octanol, while producing no detectable 3-pentanol or 3-hexanone. The mandibular gland secretions of these two species attract the workers, increase their linear speed, and reduce their sinuosity of movement. In M.schencki these behavioural activities are caused by 3-octanol and 3-octanone, the effect of a synthetic mixture of the two being exactly like that of an isolated mandibular gland; the two compounds act together to cause attraction and increase linear speed, and in synergy to reduce the workers' sinuosity of movement. In M.rugulosa , 3-octanol, 3-octanone and 6-methyl-3-octanone are the major active constituents. 3-Octanone attracts the workers, its effect being enhanced by 3-octanol; it also increases the ants' linear speed, this effect being moderated slightly by the 3-octanol. Presented together these two substances act synergistically to decrease the workers' sinuosity of movement, and reproduce exactly the overall behavioural activity of an isolated mandibular gland. The chemical and behavioural results are combined with those previously reported to explain the responses of M.rubra, M.ruginodis, M.rugulosa, M.sabuleti, M.schencki and M.scabrinodis workers to isolated mandibular glands of these species.     

The complete mitogenome of Apocheima cinerarius (Lepidoptera: Geometridae: Ennominae) and comparison with that of other lepidopteran insects

The complete mitochondrial genome (mitogenome) of a female flightless geometrid moth Apocheima cinerarius was found to be 15,722 bp in length, containing 13 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, 2 ribosomal RNA (rRNA) genes, and a control region. The A + T content of the complete mitogenome is 80.83%. The AT skew value ([A − T] / [A + T]) is 0.027. The 13 PCGs of the mitogenome start with typical ATN codons, except for cox1 with the start codon CGA. All the tRNA genes have typical cloverleaf secondary structures, except for trnSer(AGN). The secondary structures of rrnL and rrnS were predicted. Six structural domains including conserved regions (IV, V) and variable regions (I, II, III, VI) were identified in the secondary structure of rrnL. The secondary structure of rrnS consists of 3 structural domains. The control region of A. cinerarius begins with conserved motifs of “ATAGA” + 19-bp poly T. It also contains a microsatellite-like (TA)₂₆, a stem-and-loop structure, and a poly-A stretch. Phylogenetic analysis showed that Geometroidea is more closely related to Bombycoidea than to Noctuoidea. A. cinerarius is more closely related to Biston panterinaria than to Phthonandria atrilineata, which is in accordance with the conventional morphology-based classification.     

The complete mitochondrial genome of Sasakia funebris (Leech) (Lepidoptera: Nymphalidae) and comparison with other Apaturinae insects

Sasakia funebris, a member of the lepidopteran family, Nymphalidae (superfamily Papilionoidea) is a rare species and is found only in some areas of South China. In this study, the 15,233 bp long complete mitochondrial genome of S. funebris was determined, and harbors the gene arrangement identical to all other sequenced lepidopteran insects. The nucleotide composition of the genome is highly A + T biased, accounting for 81.2%. All protein-coding genes (PCGs) start with typical ATN codons, except for COI which begins with the CGA codon. All tRNAs have a typical clover-leaf secondary structure, except for tRNA^Ser(AGN), the dihydrouridine (DHU) arm of which forms a simple loop. The S. funebris A + T-rich region of 370 bp contains several features common to the Lepidoptera insects, including the motif ATAGA followed by a 19 bp poly-T stretch, and two tandem repeats consisting of 18 bp repeat units and 14 bp repeat units. The phylogenetic analyses of Apaturinae based on mitogenome sequences showed: (S. funebris + Sasakia charonda) + (Apatura metis + Apatura ilia). This result is consistent with the morphological classification.     

Changes in biomass and nutrient content of <Emphasis Type="Italic">Nymphoides hydrophylla</Emphasis> (Lour.) O. Kuntz. in a tropical pond: a comparison with other tropical and temperate species

A study was conducted to ascertain monthly changes in biomass of the plant and nutrient content in various organs of Nymphoides hydrophylla grown in a tropical pond during September 1999–August 2000 in relation to environmental factors. Biomass of N. hydrophylla ranged from 25 to 247 g dry weight m⁻². Among the various organs, leaf blade showed highest nitrogen (3.0–4.6%) and phosphorus content (0.9–2.4%). Comparative data of three Nymphoides species showed that N. peltata, the temperate species, had maximum potential of biomass production while long flowering period, year around growth, higher nitrogen content in various organs and presence of other associated flora were unique features of tropical species (N. hydrophylla and N. indica). Both water temperature and water level together appeared to be the best environmental variables that significantly explained the variability in biomass of N. hydrophylla.