海洋浮游藻类细胞质膜氧化还原活性与细胞外CA活性的关系

海洋浮游藻类除通过吸收和释放分子与离子来改变其环境的化学成分外,还可通过细胞外表面一些酶的作用引起质膜外化学物质变化。在这方面,海洋浮游藻类一个主要的细胞外表面酶-碳酸酐酶(CA),在经胰蛋白酶处理从细胞质膜上释放出来后,仍保留其催化活性。当细胞外表面CA(简称细胞外CA)具活性时,可催化质膜外HCO_3~-与CO_2的相互转化,为Rubisco(磷酸核酮糖羧化酶)提供一稳定的CO_2流量环境,以维持正常的光合作用。     

Microbial diversity of a heavily polluted microbial mat and its community changes following degradation of petroleum compounds

We studied the microbial diversity of benthic cyanobacterial mats inhabiting a heavily polluted site in a coastal stream (Wadi Gaza) and monitored the microbial community response induced by exposure to and degradation of four model petroleum compounds in the laboratory. Phormidium- and Oscillatoria-like cyanobacterial morphotypes were dominant in the field. Bacteria belonging to different groups, mainly the Cytophaga-Flavobacterium-Bacteriodes group, the gamma and beta subclasses of the class Proteobacteria, and the green nonsulfur bacteria, were also detected. In slurry experiments, these communities efficiently degraded phenanthrene and dibenzothiophene completely in 7 days both in the light and in the dark. n-Octadecane and pristane were degraded to 25 and 34% of their original levels, respectively, within 7 days, but there was no further degradation until 40 days. Both cyanobacterial and bacterial communities exhibited noticeable changes concomitant with degradation of the compounds. The populations enriched by exposure to petroleum compounds included a cyanobacterium affiliated phylogenetically with Halomicronema. Bacteria enriched both in the light and in the dark, but not bacteria enriched in any of the controls, belonged to the newly described Holophaga-Geothrix-Acidobacterium phylum. In addition, another bacterial population, found to be a member of green nonsulfur bacteria, was detected only in the bacteria treated in the light. All or some of the populations may play a significant role in metabolizing the petroleum compounds. We concluded that the microbial mats from Wadi Gaza are rich in microorganisms with high biodegradative potential.     

Microstructural observations of villous and membrane histology in monochorionic triplet placenta after in vitro fertilization

The frequency of triplet gestation is low in humans, estimated at 1:6400 deliveries. Monochorionic gestations represent a subpopulation of approximately 10% of these triplet pregnancies. Hypertensive complications are known to occur with greater frequency in the context of multiple gestation. In this report we describe microscopic placental changes associated with pre-eclampsia and proteinuria in the setting of an uncommon monochorionic-triamniotic triplet pregnancy achieved via in vitro fertilization. Histologic features observed in this case include placental stromal fibrosis and increased syncytial nodularity (Tenney-Parker change). In this triplet delivery resulting from two consecutive fissions of a single embryo, chorion and amnion configuration are also characterized with a review of the literature discussing the potential relationship between in vitro culture conditions and monozygotic multiple gestation.     

INORGANIC CARBON LIMITATION, EXOFACIAL CARBONIC ANHYDRASE ACTIVITY, AND PLASMA MEMBRANE REDOX ACTIVITY IN MARINE PHYTOPLANKTON SPECIES

In the marine phytoplankton species tested, a possible link between exofacial ferricyanide reduction at the plasma membrane of intact cells, inorganic carbon status of the cells, and extracellular carbonic anhydrase (CA) activity is proposed. In species with no extracellular CA activity under carbon-limited or carbon-replete conditions, barely detectable ferricyanide reduction was observed. Species in which extracellular CA was only detected under carbon-limited conditions showed high rates of exofacial ferricyanide reduction, as shown previously for Skeletonema costatum. Immunological analysis has demonstrated that the CA protein was present in both carbon-limited and carbon-replete cells, even though the CA activity could only be detected when inorganic carbon was limiting. Incubation of the inactive extracellular CA protein from carbon-replete cells with DTT caused activation of the enzyme. It is proposed that CA limitation in the light promotes proton extrusion and increased plasma membrane redox activity, which result in the protonation and activation of the extracellular CA.     

Characterization of a cell-type-restricted negative regulatory activity of the human granulocyte-macrophage colony-stimulating factor gene.

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates the proliferation and maturation of normal myeloid progenitor cells and can also stimulate the growth of acute myelogenous leukemia (AML) blasts. GM-CSF is not normally produced by resting cells but is expressed by a variety of activated cells including T lymphocytes, macrophages, and certain cytokine-stimulated fibroblasts and endothelial cells. Production of GM-CSF by cultured AML cells has been demonstrated, and GM-CSF expression by normal myeloid progenitors has been postulated to play a role in myelopoiesis. We have investigated the regulation of expression of GM-CSF in AML cell lines, and our results demonstrate the presence of a strong constitutive promoter element contained within 53 bp upstream of the cap site. We have also identified a negative regulatory element located immediately upstream of the positive regulatory element (within 69 bp of the cap site) that is active in AML cell lines but not T cells or K562 CML cells. Competition transfection and mobility shift studies demonstrate that this activity correlates with binding of a 45-kDa protein.     

The repeated sequence CATT(A/T) is required for granulocyte-macrophage colony-stimulating factor promoter activity.

The hematopoietic growth factor GM-CSF (granulocyte-macrophage colony-stimulating factor) is expressed by activated but not resting T lymphocytes. Previously, we localized GM-CSF-inducible promoter activity to a 90-bp region of GM-CSF 5'-flanking sequences extending from bp -53 to +37. To more precisely identify the GM-CSF DNA sequences required for inducible promoter activity in T lymphocytes, we have performed mutagenesis within a region of GM-CSF 5'-flanking sequences (bp -57 to -24) that contains the repeated sequence CATT(A/T). Mutations that do not alter the repeated CATT(A/T) sequence do not eliminate inducible promoter activity, whereas mutation or deletion of either of the CATT(A/T) repeats eliminates all inducible promoter activity in T-cell lines and in primary human T lymphocytes. Thus, both copies of the direct repeat CATT(A/T) are required for mitogen-inducible expression of GM-CSF in T cells.     

The intracellular localisation of malate dehydrogenase in Anacystis nidulans

Abstract Malate dehydrogenase has been reported to be active as a Krebs cycle enzyme in Anabaena cylindrica and Anacystis nidulans [1,2] and as an enzyme of the glycollate pathway in Anabaena cylindrica [1,3]. This enzyme was also reported in Oscillatoria spp. [4] and in Nostoc muscorum [5]. The isoenzyme of eukaryotic organisms was known to participate in various metabolic pathways and to be localized in different subcellular organelles [6–9]. Kovatcheva and Bergman [5] have purified the enzyme from the reddish-brown 20 000 × g × 20 min supernatant. We have determined the intracellular distribution of malate dehydrogenese of Anacystis nidulans and present evidence that it is largely associated with the thylakoids. The significance of this study is discussed in terms of the dual role of cyanobacterial thylakoids in photosynthesis and respiration.