Compartmentalisation of nitrogenase in a non-heterocystous cyanobacterium: Trichodesmium contortum

Abstract In Trichodesmium contortum , nitrogenase was detected in only a limited number (about 10%) of microscopically distinguishable, consecutively arranged cells in central regions of the trichomes. Cells with nitrogenase also contained the photosystem II associated pigment phycoerythrin. These cells were not distinguishable from other cells on a structural basis, but were clearly visible at low magnification microscopy as all in the zone were more compact and shorter than those on either side. The compartmentalisation of nitrogenase into a chain of cells and in a possibly photosynthetic environment represents a previously undescribed phenomenon. The nitrogenase containing cells apparently perform the O₂ protective function of heterocysts yet are different in several aspects.     

Metabolic activation and toxicity of a DDT-metabolite, 3-methylsulphonyl-DDE, in the adrenal zona fasciculata in mice

Whole-body autoradiography of 14C-labelled 3-methylsulphonyl-DDE (3-MeSO2-DDE) in female C57BL mice revealed a heavy accumulation in the adrenal cortex. Fairly high radioactivity appeared in the nasal mucosa and fat, while the labelling of the liver was intermediate. The adrenal radioactivity remained largely unextracted in tissue-sections treated with organic solvents. In the liver and intestinal contents the radioactivity was partly extracted, whereas in all other tissues almost completely extracted. According to light microscopic autoradiography, the tissue-bound adrenal radioactivity was confined to the zona fasciculata, leaving the other adrenal zones devoid of bound material. Incubation of 3-MeSO2-DDE with adrenal tissue (300 X g supernatant) revealed a dose- and time-dependent covalent binding to protein and formation of water-soluble metabolites. The cytochrome P-450 inhibitors metyrapone and carbon monoxide inhibited both covalent binding and polar metabolite formation. Addition of reduced glutathione decreased binding, while polar metabolite formation was increased. Histopathological examination of adrenals from 3-MeSO2-DDE-treated mice revealed extensive vacuolation and necrosis of the zona fasciculata 1-12 days after single doses down to 25 mg/kg. Degenerative changes were observed at 12.5 mg/kg. In contrast to 3-MeSO2-DDE, 14C-labelled 3,3'-bis(methylsulphonyl)-DDE was not accumulated in the adrenal cortex. 3-MeSO2-DDE is thus a persistent environmental pollutant with a unique ability to produce acute toxicity subsequent to metabolic activation in a mammalian tissue.     

Integrated control of hepatic glucose metabolism.

The rates of storage and release of carbohydrate by the liver are determined by the plasma concentrations of several blood-borne signals; most important are the concentrations of glucose, and of the hormones insulin and glucagon. To understand the complex control relationships of these three signals as they affect the liver, their individual dynamic influences have been determined experimentally, and the findings have been integrated by means of a computer simulation of the pathways of hepatic glycogen metabolism. The simulation studies have led to specific hypotheses about the biochemical effects of glucose and insulin on the liver. The simulation studies have also led to the conclusion that glucose exerts a rapid moment-to-moment influence on the rate of uptake of glucose by the liver. Insulin, however, by exerting a slower influence on the sensitivity of the liver to glucose, is very effective in "optimizing" the amount of glycogen which the liver stores during food intake. Thus, integrated experimental and simulation studies can lead to a view of a physiological regulating system which does not emerge from either approach used alone.-     

Neurohypophyseal hormone-responsive renal adenylate cyclase. IV. A random-hit matrix model for coupline in a hormone-sensitive adenylate cyclase system

A "random-hit" matrix model is proposed to account for the dynamic and steady state relationship between occupation of bovine renal medullary membrane receptors by [Lys8]vasopressin (LVP) and neurohypophyseal hormones (NHH) and the associated activation of membrane-bound adenylate cyclase. The model was developed by systematic introduction of specific rules concerning receptor coupling into a general structural model which consists of two square matrices of identical size, one composed of homogeneous R ("receptor") units, the second of homogeneous C ("cyclase") units. R units are either occupied (RO) or unoccupied (RU); C units are either active (CA) or inactive (CI). Hormone molecules are envisioned to "collide" with R units randomly; collision with RU leads to "binding", and occupation is maintained for a characteristic mean occupancy time, TO. In this structure, each R unit has an "interaction field" which consists of the "twin" unit in the "C" matrix, and the 4 nearest neighbor C units surrounding the twin. Occupation of an R unit leads to activation of all CI units in the interaction field of that R; CA units in the interaction field are refractory. Thus binding at a given R may "recruit" a variable number of inactive neighboring C units (5, 4, 3, 2, 1, or 0). The model requires that there be individual coupling delays between the moment of binding at a given R and subsequent activation of CI units (mean coupling delay (Td) approximately 10% To). Activation of C units persists as long as the "parent" R is occupied and is maintained for an additional short time interval (Tp) after RO reverts to RU, corresponding to hormone dissociation from receptor. The model accounts for the following previously demonstrated relations between LVP occupation of receptors and adenylate cyclase activation in bovine renal medullary membranes: 1) the shape of the nonlinear steady state relation between normalized (percentage maximal) receptor occupation (O) and cyclase activation (A), uniformly observed in different membrane preparations: 2) variable hormone concentration-dependent trajectories of approach to the final steady state A:O value (A:Oss) which may be either monophasic or biphasic; 3) the loss of intrinsic adenylate cyclase activity observed in bovine membranes for a series of NHH analogs with progressively diminishing affinity for receptors. The model represents an explicit theory of coupling where a successive series of temporal events are quantitatively related to each other and privide major constraints to any interpretation of the molecular organization of receptors and adenylate cyclase units in membranes. The model excludes a number of mechanistic proposals and suggests a new hypothesis for membrane coupling with features which may be generally applicable to other hormone-sensitive adenylate cyclase systems.     

Competitive Advantage Provided by Bacterial Motility in the Formation of Nodules by Rhizobium meliloti

The effect of motility on the competitive success of Rhizobium meliloti in nodule production was investigated. A motile strain formed more nodules than expected when mixed at various unfavorable ratios with either flagellated or nonflagellated nonmotile derivatives. We conclude that motility confers a selective advantage on rhizobia when competing with nonmotile strains.     

Quantitative affinity chromatography: increased versatility of the technique for studies of ligand binding

The potential of affinity chromatography for the characterization of strong solute-ligand interactions is explored by studying the NADH-dependent elution of rabbit muscle lactate dehydrogenase from a column of trinitrophenyl-Sepharose in 0.067 M phosphate, pH 7.2. An interesting development is the simplification of the general affinity chromatography theory that emanates from the use of affinity matrices with a high concentration of immobilized reactant groups. The resultant expression allows evaluation of the intrinsic association constant for solute-ligand interactions from a single series of either zonal or frontal affinity chromatographic experiments conducted in the presence of a range of free ligand concentrations. Thus, contrary to previous belief, an affinity matrix designed for solute purification work should prove to be an asset for, rather than an impediment to, the study of solute-ligand interactions by quantitative affinity chromatography.     

Kinship and Dominance Rank Influence the Strength of Social Bonds in Female Geladas (Theropithecus gelada)

In many primates, close social relationships are associated with lower stress, better health, and increased life span. However, individuals do not form bonds indiscriminately; rather, they focus on a few primary partners. This suggests that the identity of the partner may be as important as the bond itself. Although dominance and kinship have repeatedly emerged as salient predictors of female relationships, most of this research comes from species with multimale, multifemale groups and strict dominance hierarchies. Further, kinship was typically determined based on either behavior or on known mother–daughter relationships alone. To understand the generality of previous findings, we use behavioral and genetic sampling to examine whether dominance rank and/or genetic relatedness mediate female social bonds in geladas (Theropithecus gelada) living in the Simien Mountains National Park, Ethiopia. First, we found that, even though females in the same unit are closely related, female geladas still preferentially bond with the closest of these relatives. Second, females that were close kin formed the strongest bonds with females of similar rank to themselves. Finally, rank disparity predicted grooming rates but did not predict whether females were nearest neighbors. This suggests that, in contrast with data from other cercopithecines, spatial proximity among females may be less indicative of strong social bonds for geladas, a species that routinely exhibits a high degree of spatial overlap with extra-unit individuals. Together, these results highlight the importance of combining genetic data with detailed behavioral observations to help us understand how individuals choose and interact with social partners.     

UNICELLULAR CYANOBIONTS IN OPEN OCEAN DINOFLAGELLATES,RADIOLARIANS, AND TINTINNIDS: ULTRASTRUCTURAL CHARACTERIZATION AND IMMUNO‐LOCALIZATION OF PHYCOERYTHRIN AND NITROGENASE1

Cyanobacterial symbionts (cyanobionts) have been identified forming associations with various open ocean eukaryotic host genera, including two dinophysoid genera, Histioneis sp. and Ornithocercus sp., two radiolarians, Spongastaurus and Dictyocoryne truncatum, sp., and a tintinnid, Codonella sp. The TEM analysis revealed that single individual hosts were closely associated with one to two different cyanobacterial morphotypes (cyanobionts) and two hosts had in addition to cyanobionts, one to two bacterial cell types. Eleven significantly (P<0.01) different cell types were identified as cyanobionts, with cell diameters ranging 0.5±0.38–3.7±0.66 μm. Using immunogold‐labeling techniques coupled to the TEM, four of the five cell types contained phycoerythrin (PE) at high levels (>71±28 gold particles·μm^?2). Immunolabeling‐TEM using nitrogenase antisera demonstrated a significant (P<0.01) nitrogenase content in cell type four cyanobionts of Histioneis sp. host 1 (39±34 gold particles·μm^?2). The cyanobionts of the radiolarians were of a cell diameter (0.5–0.8 μm) and showed ultrastructural characters (peripheral thylakoids) reminiscent of Prochlorococcus sp. Also, an open ocean tintinnid, Codonella sp., was shown to contain cyanobacteria as symbionts for the first time. In all cyanobionts, glycogen storage was obvious, no cellular degradation was visible, cells were observed in the process of cellular division, and antisera localization was apparent. These observations suggest that the relationship between host eukaryote and cyanobacteria is an active one, and likely symbiotic.     

Host Erythrocyte Environment Influences the Localization of Exported Protein 2, an Essential Component of the Plasmodium Translocon

Malaria parasites replicating inside red blood cells (RBCs) export a large subset of proteins into the erythrocyte cytoplasm to facilitate parasite growth and survival. PTEX, the parasite-encoded translocon, mediates protein transport across the parasitophorous vacuolar membrane (PVM) in Plasmodium falciparum-infected erythrocytes. Proteins exported into the erythrocyte cytoplasm have been localized to membranous structures, such as Maurer''s clefts, small vesicles, and a tubovesicular network. Comparable studies of protein trafficking in Plasmodium vivax-infected reticulocytes are limited. With Plasmodium yoelii-infected reticulocytes, we identified exported protein 2 (Exp2) in a proteomic screen of proteins putatively transported across the PVM. Immunofluorescence studies showed that P. yoelii Exp2 (PyExp2) was primarily localized to the PVM. Unexpectedly, PyExp2 was also associated with distinct, membrane-bound vesicles in the reticulocyte cytoplasm. This is in contrast to P. falciparum in mature RBCs, where P. falciparum Exp2 (PfExp2) is exclusively localized to the PVM. Two P. yoelii-exported proteins, PY04481 (encoded by a pyst-a gene) and PY06203 (PypAg-1), partially colocalized with these PyExp2-positive vesicles. Further analysis revealed that with P. yoelii, Plasmodium berghei, and P. falciparum, cytoplasmic Exp2-positive vesicles were primarily observed in CD71⁺ reticulocytes versus mature RBCs. In transgenic P. yoelii 17X parasites, the association of hemagglutinin-tagged PyExp2 with the PVM and cytoplasmic vesicles was retained, but the pyexp2 gene was refractory to deletion. These data suggest that the localization of Exp2 in mouse and human RBCs can be influenced by the host cell environment. Exp2 may function at multiple points in the pathway by which parasites traffic proteins into and through the reticulocyte cytoplasm.