土地处理系统中悬浮固体的整体分析技术研究

1 前言 土地处理系统对悬浮固体具有很好的净化效果,其净化率要害99%以上,但实际过程中,一些干扰     

Molecular basis for the interaction of histamine with the histamine H2 receptor.

We undertook these studies to characterize the molecular basis of the interaction of histamine with the H2 receptor. Key areas of homology in the structures of the histamine H2 and beta 2 adrenergic receptor suggested specific transmembrane amino acids that might be important for binding of histamine. A third transmembrane aspartic acid of the histamine receptor (Asp98), thought to serve as a counter anion that interacts with the cationic amine moiety of histamine, was mutated to Asn98, and the mutated receptor was expressed in Hepa cells. Removal of the negatively charged amino acid abolished both binding of the H2 receptor antagonist [methyl-3H]tiotidine and histamine stimulated increases in cellular cAMP content. Mutation of a fifth transmembrane aspartic acid (Asp186) to Ala186 or Asn186 by itself or in conjunction with mutation of another fifth transmembrane amino acid (Thr190 to Ala190) resulted in a loss of [methyl-3H] tiotidine binding, although the generation of cAMP in response to histamine was maintained. The histamine receptor with only a Thr190 to Ala190 or Cys190 mutation retained the ability to bind [methyl-3H]tiotidine, but both the affinity and efficacy of binding were reduced. These data lead us to propose a model for histamine binding in which Asp98 is essential for histamine binding and action, Asp186 defines H2 selectivity, and Thr190 is important in establishing the kinetics of histamine binding, but is not essential for H2 selectivity.     

Adenine affects the structure and stability of telomeric sequences.

Adenine occurs in the strand containing repeated G clusters in the telomeric DNA of a variety of organisms, including that of humans. The role of adenine has been investigated by constructing two sets of oligonucleotides each with one, two, or four copies of the telomeric sequence dTTTAGGG together with a control sequence in which T replaces the A residue, dTTTTGGG. Comparison of the stability and spectral properties of these two sequences in the presence of Na+ or K+ affords a basis for defining the role of adenine in these structures. In Na+, the A residue stabilizes the structure formed by each oligomer significantly, presumably by a base-pairing interaction with T. In K+, by contrast, there is little difference in stability. In two- and four-copy oligomers, the A sequence has a different structure from its T analog, as detected by CD spectroscopy. In the presence of either Na+ or K+, the tetraplexes of A and T interact with intercalators.     

Medial edge epithelium fate traced by cell lineage analysis during epithelial-mesenchymal transformation in vivo.

Vital cell labeling techniques were used to trace the fate of the medial edge epithelial (MEE) cells during palatal fusion in vivo. Mouse palatal tissues were labeled in utero with DiI. The fetuses continued to develop in utero and tissues of the secondary palate were examined at several later stages of palatal ontogeny. The presence and distribution of DiI was correlated with the presence of cell phenotype-specific markers. During the initial stages of palatal fusion the DiI-labeled MEE were present in the midline position. These cells were attached to an intact laminin-containing basement membrane and contained keratin intermediate filaments. At later stages of palatogenesis the DiI-labeled MEE were not separated from the mesenchyme by an intact basement membrane and did not contain keratin. In late fetal development, DiI-labeled cells without an epithelial morphology were present in the mesenchyme. The transition of the DiI-labeled cells from an epithelial phenotype to a mesenchymal phenotype is consistent with a fate of epithelial-mesenchymal transformation rather than programmed cell death.     

Interactions of a laminin-binding peptide from a 33-kDa protein related to the 67-kDa laminin receptor with laminin and melanoma cells are heparin-dependent.

A laminin-binding peptide (peptide G), predicted from the cDNA sequence for a 33-kDa protein related to the 67-kDa laminin receptor, specifically inhibits binding of laminin to heparin and sulfatide. Since the peptide binds directly to heparin and inhibits interaction of another heparin-binding protein with the same sulfated ligands, this inhibition is due to direct competition for binding to sulfated glycoconjugates rather than an indirect effect of interaction with the binding site on laminin for the 67-kDa receptor. Direct binding of laminin to the peptide is also inhibited by heparin. This interaction may result from contamination of the laminin with heparan sulfate, as binding is enhanced by the addition of substoichiometric amounts of heparin but inhibited by excess heparin and two heparin-binding proteins. Furthermore, laminin binds more avidly to a heparin-binding peptide derived from thrombospondin than to the putative receptor peptide. Adhesion of A2058 melanoma cells on immobilized peptide G is also heparin-dependent, whereas adhesion of the cells on laminin is not. Antibodies to the beta 1-integrin chain or laminin block adhesion of the melanoma cells to laminin but not to peptide G. Thus, the reported inhibition of melanoma cell adhesion to endothelial cells by peptide G may result from inhibition of binding of laminin or other proteins to sulfated glycoconjugate receptors rather than from specific inhibition of laminin binding to the 67-kDa receptor.     

Increased Activity of a Cationic Peroxidase Associated with an Incompatible Interaction Between Xanthomonas oryzae pv oryzae and Rice (Oryza sativa)

Rice (Oryza sativa L.) cultivar Cas 209 carries the gene Xa-10 for resistance to race 2 of Xanthomonas oryzae pv oryzae, the bacterial blight pathogen. When seedling leaves of Cas 209 plants were infiltrated with bacterial cell suspensions of strain PXO86^Rif (race 2, incompatible), total peroxidase activity in extracts from extracellular spaces increased almost threefold between 16 and 24 hours after inoculation. The increase in total peroxidase activity in extracellular extracts was correlated with the appearance of a 43-kilodalton peroxidase isoenzyme with an isoelectric point of 8.6. Increases in the activities of two anionic peroxidase isoenzymes also were associated with the incompatible interaction. Later during the interactions, total peroxidase activities increased in both compatible (cv Cas 209 infiltrated with race 1, PXO61^Sm) and control (Cas 209 infiltrated with water) treatments, but final activity levels were less than that observed in the incompatible combination. Similarly, the cationic peroxidase was detected in all three treatments by 48 hours after infiltration, but at reduced levels in compatible and water-infiltrated control treatments relative to the incompatible combination. Accumulation of this peroxidase in extracellular spaces thus may play a role in the defense response in cultivar Cas 209.     

Conformational preference and ligand binding properties of DNA junctions are determined by sequence at the branch

Four-arm DNA branched junctions are stable analogues of Holliday recombinational intermediates. A number of four-arm DNA junctions synthesized from oligonucleotides have now been studied. Gel mobility or chemical footprinting experiments on several immobile four-arm junctions indicate that in the presence of Mg2+, they assume a preferred conformation consisting of two helical domains, each formed by stacking a particular pair of arms on each other. We show here that a junction we designate as J1c that has the same chemical composition as one we have previously studied in detail, J1, but is formed from the four strands complementary to those of the latter, exhibits the reverse stacking preference. The pattern of self-protection of the strands of J1c exposed to Fe(II).EDTA-induced scission reveals that twofold symmetry is preserved, but the opposite pair of strands preferentially cross over. Moreover, the Fe(II).EDTA scission profiles of J1c indicate that this junction exhibits a weaker bias as to which strands cross over than is observed in J1. The preference for the dominant species in J1 is 1.3 times greater than in J1c at 4 degrees C and in the presence of 10 mM Mg2+, based on chemical reactivity data. This is confirmed by a cleavage experiment using the resolvase enzyme, endonuclease I, from bacteriophage T7. This difference could reflect either sequence-dependent differences in the equilibrium among isomers, or in the structure of these junctions. Chemical footprinting experiments using the probes MPE.Fe(II) and (OP)2Cu(I) show that the high-affinity ligand binding site in immobile junctions is determined by junction geometry.     

Regulated temporal and spatial expression of the calcium-binding proteins calcyclin and OPN (osteopontin) in mouse tissues during pregnancy.

In situ hybridization and northern/slot blot analyses were used to quantify the expression of calcyclin (2A9, 5B10), osteopontin (opn, secreted phosphoprotein, 2ar) and calmodulin mRNAs in mouse tissues that support pregnancy. High-to-moderate levels of the mRNAs of all three genes were detected at discrete locations in the uterus, decidua and placenta as a function of gestation time. Calmodulin expression was constant in these tissues; calcyclin mRNA was high during early pregnancy and declined after day 8-9 of gestation; and opn mRNA was undetectable before day 7, with maximal levels on days 9-12 in each of these tissues. Calcyclin, but not opn, expression was also observed in the chorioamnion after day 12. Calcyclin was expressed throughout the decidua on day 8 but became restricted to the primary (antimesometrial) decidual zone and decidua lateralis on day 9, and the decidua capsularis after day 9. By contrast, opn mRNA was localized on day 9 to the mesometrial triangle, which contains a large population of granulated metrial gland cells, and to the decidua basalis. These two genes may serve as markers for the two types of decidual tissue. We suggest that one function of OPN, which may be an indicator of cells in the decidua that have a bone marrow genealogy, is to mediate the flux of calcium from the maternal circulation to the developing embryo.