A SURVEY FOR 1,3,6,7-TETRAHYDROXY-C-GLYCOSYLXANTHONES EMPHASIZING THE “PRIMITIVE” LEPTOSPORANGIATE FERNS AND THEIR ALLIES

A survey for 1,3,6,7-tetrahydroxy-C-glycosylxanthones of representative species within the primitive vascular plants, emphasizing the leptosporangiate ferns, has indicated a limited distribution of these compounds within three leptosporangiate families: Hymenophyllaceae, Aspleniaceae and Marsileaceae. In the Hymenophyllaceae the distribution of these compounds appears to be a useful criterion for segregating species of Mecodium from other species of Hymenophyllum (sensu lato) and suggests that the tubulate vs. the valvate indusial condition may not be an ideal character for separating all species of Hymenophyllum (s.l.) from those of Trichomanes (s.l.). These compounds appear useful for delimiting several species of Elaphoglossum section Pachyglossa and support a relationship among the Aspleniaceae, Athyriaceae, and Elaphoglossaceae. Their presence in Marsilea also raises questions as to the origin of this group of plants.     

机械损伤对9种水生植物叶片的影响

水生植物叶片的功能性状特征与陆生植物有所不同,同时叶脉类型也显著影响叶片的功能性状。本研究选取9种具有不同叶脉类型的水生植物,通过对叶脉进行直接损伤,分析叶片性状（形态、色素含量和叶绿素荧光指标）在叶脉受损后的变化程度与叶脉类型的关系。结果显示：具有平行脉的3种水生植物对叶脉损伤具有较强的耐受性;具羽状脉的4种植物主脉受损后显著抑制叶片生长,而侧脉受损的影响在不同物种间有所不同,具有物种特异性。本研究可为大型湖泊水生植物修复的水生物种筛选提供参考。     

Plasminogen activation by receptor-bound urokinase. A kinetic study with both cell-associated and isolated receptor

The specific cellular receptor for urokinase-type plasminogen activator (uPA) is found on a variety of cell types and has been postulated to play a central role in the mediation of pericellular proteolytic activity. We have studied the kinetics of plasminogen (Plg) activation catalyzed by uPA specifically bound to its receptor on the human monocytoid cell-line U937 and demonstrate this process to have properties differing widely from those observed for uPA in solution. The solution-phase reaction was characterized by a Km of 25 microM and for the cell-associated reaction this fell 40-fold to 0.67 microM, below the physiological Plg concentration of 2 microM. A concomitant 6-fold reduction in kcat resulted in an increase in the overall catalytic efficiency, kcat/Km, of 5.7-fold. This high affinity Plg activation was abolished in the presence of a Plg-binding antagonist. In contrast to intact cells, purified uPA receptor (isolated from phorbol 12-myristate 13-acetate-stimulated U937 cells) was observed to partially inhibit uPA-catalyzed Plg activation, although activity against low molecular weight substrates was retained. Therefore, the cellular binding of Plg appears to be of critical importance for the efficient activation of Plg by receptor-bound uPA. Plasmin generated in the cell-surface Plg activation system described here was also observed to be protected from its principal physiological inhibitor alpha-2-antiplasmin. Together, these data demonstrate that the cell surface constitutes the preferential site for Plg activation when uPA is bound to its specific cellular receptor, which therefore has the necessary characteristics to play an efficient role in the generation of pericellular proteolytic activity.     

Complementation between urokinase-producing and receptor-producing cells in extracellular matrix degradation.

The respective roles of urokinase plasminogen activator (u-PA) and the u-PA receptor in extracellular matrix degradation was investigated. Human pro-u-PA and the human u-PA receptor were expressed independently by two different mouse LB6 cell lines. The matrix degradation capacity of these cell lines individually or in coculture was studied. Although pro-u-PA-producing cells alone degrade the matrix in the presence of plasminogen, u-PA-receptor producing cells do not. Cocultivation of a small fraction of pro-u-PA-producing cells with the receptor-producing cells increases the rate of matrix degradation at least threefold. By immunoprecipitation it was shown that cocultivation of the two cell lines increases the conversion of the inactive pro-u-PA to the active two chain u-PA. The enhancement of matrix degradation and of pro-u-PA activation requires actual binding of pro-u-PA to its receptor because it is inhibited by u-PA-receptor antagonists. The u-PA receptor must be cell associated, as binding of pro-u-PA to a receptor solubilized from the cell surface with phosphatidyl-inositol specific phospholipase C did not enhance the activation of pro-u-PA in the presence of plasminogen. The finding that activity of u-PA is enhanced when it is bound to its receptor, even when the receptor is produced by a different cell, might have important implications for the mechanisms of u-PA-induced extracellular proteolysis in vivo.     

Nucleotide sequence of a cDNA from Onchocerca gibsoni encoding a novel repetitive antigen.

mRNA from uterine microfilariae of the cattle parasite Onchocerca gibsoni was used for the construction of cDNA libraries. A cDNA clone encoding an antigen recognized by serum from human individuals infected with O. volvulus was found to contain five copies of an 87 bp unit. These 87 bp units were present in the genome in high copy number as long tandem arrays. These are the first cDNA sequence data obtained directly from larvae of any Onchocerca species.     

Identification and characterization of the murine cell surface receptor for the urokinase-type plasminogen activator.

Cell-binding experiments have indicated that murine cells on their surface have specific binding sites for mouse urokinase-type plasminogen activator (u-PA). In contrast to the human system, chemical cross-linking studies with an iodinated ligand did not yield any covalent adducts in the murine system, but in ligand-blotting analysis, two mouse u-PA-binding proteins could be visualized. To confirm that these proteins are the murine counterpart of the human u-PA receptor (u-PAR), a peptide was derived from the murine cDNA clone assigned to represent the murine u-PAR due to cross-hybridization and pronounced sequence similarity with human u-PAR cDNA [Kristensen, P., Eriksen, J., Blasi, F. & Dan?, K. (1991) J. Cell Biol. 115, 1763-1771]. A rabbit antiserum raised against this peptide specifically recognized two polypeptide bands with electrophoretic mobilities identical to those identified by ligand-blotting analysis. Binding of mouse u-PA to its receptor showed species specificity in ligand-blotting analysis, since mouse u-PA did not bind to human u-PAR and human u-PA did not bind to mouse u-PAR. The apparent M(r) of mouse u-PAR varied between different mouse cell lines and ranged over M(r) 45,000-60,000. In four of the cell lines, mouse u-PA bound to two mouse u-PAR variant proteins, whereas in the other two cell lines studied, there was only one mouse u-PA-binding protein. In the monocyte macrophage cell line P388D.1, trypsin-treatment of intact cells could remove only the large mouse u-PAR variant (M(r) 60,000) indicating that only this type was a cell-surface-exposed molecule. The smaller mouse u-PAR variant (M(r) 45,000), was deglycosylated by the enzyme endo-beta-N-acetylglucosaminidase H and is probably an intracellular precursor form carrying only high-mannose carbohydrate. Deglycosylation of this variant yielded a polypeptide with an apparent M(r) of about 30,000, which corresponds to the Mr calculated from the cDNA derived protein sequence of mouse u-PAR. Receptor-bound mouse u-PA could be released by phosphatidylinositol-specific phospholipase C treatment, indicating that mouse u-PAR is attached to the cell surface by glycosylphosphatidylinositol. Purification of the two mouse u-PAR variant proteins by diisopropylfluorophosphate-inactivated mouse u-PA-Sepharose affinity chromatography yielded two silver-stained bands when analysed by SDS/PAGE, corresponding in electrophoretic mobility to those seen by ligand-blotting analysis.(ABSTRACT TRUNCATED AT 400 WORDS)     

A soluble form of the glycolipid-anchored receptor for urokinase-type plasminogen activator is secreted from peripheral blood leukocytes from patients with paroxysmal nocturnal hemoglobinuria.

The cellular urokinase-type plasminogen-activator (uPA) receptor (uPAR) is a glycolipid-anchored membrane protein thought to be involved in pericellular proteolysis during cell migration and tumor invasion. In the present study, we have identified and characterized two soluble forms of uPAR which have retained their ligand-binding capability. One variant was generated in vitro by treatment of intact normal cells with either a phosphatidylinositol-specific phospholipase C (PLC) or endoproteinase Asp-N. The other soluble uPAR variant was secreted in vivo from peripheral blood leukocytes affected by the stem-cell disorder paroxysmal nocturnal hemoglobinuria (PNH), and was found in the plasma from these PNH patients as well as in the conditioned medium from cultured PNH leukocytes. Under normal conditions, we find no evidence for any shedding or secretion of a soluble uPA-binding counterpart to human uPAR in plasma. Unlike normal leukocytes, the PNH-affected cells do not express uPAR on the cell surface, although they do contain apparently normal levels of uPAR-specific mRNA. The secreted uPAR derived from PNH cells has a mobility in SDS/PAGE that is slightly higher than that of uPAR solubilized by PtdIns-specific PLC or detergent, but resembles that of a truncated, recombinant uPAR variant, which has its C-terminus close to the proposed glycolipid-attachment site, suggesting that the secreted protein has been proteolytically processed for glycolipid attachment. The presence in plasma from PNH patients of such a secreted, hydrophilic form of uPAR lends support to the hypothesis that the lesion underlying the PNH disorder resides either in glycolipid biosynthesis or in the function of an as-yet-unidentified transamidating enzyme assumed to cleave and assemble the truncated uPAR with the preformed glycolipid moiety.