By making use of the capacity of phospholipase A2 to degrade selectively the phospholipid in the outer half of the lipid bilayer of small unilamellar phospholipid/cholesterol vesicles without affecting the retention of a vesicle-encapsulated solute, we demonstrated that the exchange of phosphatidylcholine between such vesicles and human high density lipoprotein involves exclusively the phosphatidylcholine present in the outer monolayer of the vesicle membrane. 相似文献
Desulfovibrio vulgaris Hildenborough contains a family of genes for methyl-accepting chemotaxis proteins (MCPs). Here we report the complete sequence of the gene for Desulfovibrio chemoreceptor H (dcrH). The deduced amino acid sequence of DcrH protein, which has an enlarged N-terminal, ligand binding domain, indicates a structure similar to that of other MCPs. Comparison of the sequences for DcrA, determined earlier, and DcrH indicated that similarity is essentially limited to the C-terminal excitation region. The dcr gene family differs, in this respect, from mcp gene families in other eubacteria (e.g. Escherichia coli and Bacillus subtilis), where MCPs share significant homology throughout their C-terminal signal transduction domains. This may point to an ancient evolutionary origin of the dcr gene family, which is widely distributed throughout the genus Desulfovibrio. The evolutionary origin of mcp genes was traced by comparing nucleotide sequences for the excitation region that is common to all MCPs. Phylogenetic analysis of sequences for thirty mcp genes from nine eubacterial and one archaebacterial species suggested that multiplication of mcp genes has occurred at least twice since the eubacteria diverged from the archaebacteria.Nucleotide accession number: The nucleotide sequence reported in this paper has been entered into GenBank under accession number U30319. Phone: 403-220-6388. Fax: 403-289-9311. Electronic mail address: voordouw@acs.ucalgary.ca. 相似文献
Endoglucanase of Aspergillus niger AS-101 was partially purified by ammonium sulphate fractionation and molecular sieving on Sephadex G-200. The enzyme was found to be unstable on storage, however, it received some protection on the addition of BSA, glycerol or sodium azide. Glycerol also protected the enzyme from inactivation due to freezing and thawing. Studies on the effect of thiol group reagents revealed the involvement of -SH group(s) at the active site of enzyme. The enzyme was a metallo-protein or it required certain metal ions for activation. A variety of modulators such as macroionic compounds and metal ions showed varying effects on the purified endoglucanase. 相似文献
125I-labeled albumin or poly(vinyl pyrrolidone) encapsulated in intermediate size multilamellar or unilamellar liposomes with 30–40% of cholesterol were injected intravenously into rats. In other experiments liposomes containing phosphatidyl[Me-14C]choline were injected. 1 h after injection parenchymal or non-parenchymal cells were isolated. Non-parenchymal cells were separated by elutriation centrifugation into a Kupffer cell fraction and an endothelial cell fraction. From the measurements of radioactivities in the various cell fractions it was concluded that the liposomes are almost exclusively taken up by the Kupffer cells. Endothelial cells did not contribute at all and hepatocytes only to a very low extent to total hepatic uptake of the 125I-labels. Of the 14C-label, which orginates from the phosphatidylcholine moiety of the liposomes, much larger proportions were recovered in the hepatocytes. A time-dependence study suggested that besides the involvement of phosphatidylcholine exchange between liposomes and high density lipoprotein, a process of intercellular transfer of lipid label from Kupffer cells to the hepatocytes may be involved in this phenomenon. Lanthanum or gadolinium salts, which effectively block Kupffer cell activity, failed to accomplish an increase in the fraction of liposomal material recovered in the parenchymal cells. This is compatible with the notion that liposomes of the type used in these experiments have no, or at most very limited, access to the liver parenchyma following their intravenous administration to rats. 相似文献
When rats are given freedom of dietary choice, the quantity and composition of the diet selected varies from animal to animal,
but the risk to the individual of developing a variety of neoplasms is greatly increased over that of rats fed fixed diets.
The increase in frequency of tumors cannot be explained on the basis of the amount or the composition of the diet selected.
However, the application of “variable selection” statistical procedures shows that there are combinations of temporal-specific
interacting dietary and dietary-dependent variables that are closely linked with cancer mortality. The multi-variable statistical
model for animals dying with one type of tumor is not applicable to those dying with tumors of other types or sites. In every
case, the only data required to characterize the dates of death of tumor-bearing individuals are those describing the dietary
practices and growth responses prior to maturity. The model for animals with pancreatic tumors is used to illustrate the extent
to which dietary practices of early life are linked with the animals’ survival. 相似文献
Incorporation of 8 mol percent lactosylceramide into small unilamellar vesicles consisting of cholesterol and sphingomyelin in an equimolar ratio and containing [3H]inulin as a marker resulted in an increase in total liver uptake and a drastic change in intrahepatic distribution of the liposomes after intravenous injection into rats. The control vesicles without glycolipid accumulated predominantly in the hepatocytes, but incorporation of the glycolipid resulted in a larger stimulation of Kupffer-cell uptake (3.2-fold) than of hepatocyte uptake (1.2-fold). Liposome preparations both with and without lactosylceramide in which part of the sphingomyelin was replaced by phosphatidylserine, resulting in a net negative charge of the vesicles, were cleared much more rapidly from the blood and taken up by the liver to higher extents. The negative charge had, however, no influence on the intrahepatic distributions. The fast hepatic uptake of the negatively charged liposomes allowed competition experiments with substrates for the galactose receptors on liver cells. Inhibition of blood clearance and liver uptake of lactosylceramide-containing liposomes by indicated the involvement of specific recognition sites for the liposomal galactose residues. This inhibitory effect of was shown to be mainly the result of a decreased liposome uptake by the Kupffer cells, compatible with the reported presence of a galactose specific receptor on this cell type (Kolb-Bachofen et al. (1982) Cell 29, 859–866). The difference between the results on sphingomyelin-based liposomes as described in this paper and those on phosphatidylcholine-based liposomes as published previously (Spanjer and Scherphof (1983) Biochim. Biophys. Acta 734, 40–47) are discussed. 相似文献
Rhodobacter sphaeroides is a metabolically versatile bacterium capable of producing terpenes natively. Surprisingly, terpene biosynthesis in this species has always been investigated in complex media, with unknown compounds possibly acting as carbon and nitrogen sources. Here, a defined medium was adapted for R. sphaeroides dark heterotrophic growth, and was used to investigate the conversion of different organic substrates into the reporter terpene amorphadiene. The amorphadiene synthase was cloned in R. sphaeroides, allowing its biosynthesis via the native 2-methyl-d-erythritol-4-phosphate (MEP) pathway and, additionally, via a heterologous mevalonate one. The latter condition increased titers up to eightfold. Consequently, better yields and productivities to previously reported complex media cultivations were achieved. Productivity was further investigated under different cultivation conditions, including nitrogen and oxygen availability. This novel cultivation setup provided useful insight into the understanding of terpene biosynthesis in R. sphaeroides, allowing to better comprehend its dynamics and regulation during chemoheterotrophic cultivation.