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141.
Summary A series of investigations were conducted with the objective of elucidating natural pathways of electron transport from respiratory
processes to the site of N2 fixation in nodule bacteroids. A survey of dehydrogenase activities in a crude extract of soybean nodule bacteroids revealed
relatively high activities of NAD-specific β-hydroxybutyrate and glyceraldehyde-3-phosphate dehydrogenases. Moderate activities
of NADP-specific isocitrate and glucose-6-phosphate dehydrogenases were observed. By use of the ATP-dependent acetylene reduction
reaction catalyzed by soybean bacteroid nitrogenase, and enzymes and cofactors from bacteroids and other sources, the following
sequences of electron transport to bacteroid nitrogenase were demonstrated: (1) H2 to bacteroid nitrogenase in presence of a nitrogenase-free extract ofC. pasteurianum; (2) β-hydroxybutyrate to bacteroid nitrogenase in a reaction containing β-hydroxybutyrate dehydrogenase, NADH dehydrogenase,
NAD and benzyl viologen; (3) β-hydroxybutyrate dehydrogenase, to nitrogenase in reaction containing NADH dehydrogenase, NAD
and either FMN or FAD; (4) light-dependent transfer of electrons from ascorbate to bacteroid nitrogenase in a reaction containing
photosystem I from spinach chloroplasts, 2,6-dichlorophenolindophenol, and either azotoflavin from Azotobacter or non-heme
iron protein from bacteroids; (5) glucose-6-phosphate to bacteroid nitrogenase in a system that included glucose-6-phosphate
dehydrogenase, NADP, NADP-ferredoxin reductase from spinach, azotoflavin from Azotobacter and bacteroid non-heme iron protein.
The electron transport factors, azotoflavin and bacteroid non-heme iron protein, failed to function in the transfer of electrons
from an NADH-generating system to bacteroid nitrogenase. When FMN or FAD were added to systems containing azotoflavin and
bacteroid non-heme iron protein, electrons apparently were transferred to the flavin-nucleotides and then nitrogenase without
involvement of azotoflavin and bacteroid non-heme iron protein.
Evidence is available indicating that nodule bacteroids contain flavoproteins analogous to Azotobacter, azotoflavin, and spinach
ferredoxin-NADP reductase. It is concluded that physiologically important systems involved in transport of electrons from
dehydrogenases to nitrogenase in bacteroids very likely will include relatively specific electron transport proteins such
as bacteroid non-heme iron protein and a flavoprotein from bacteroids that is analogous to azotoflavin. 相似文献
142.
Mr. R. J. Sterling J. M. Gasc P. J. Sharp J. M. Renoir P. Tuohimaa E. E. Baulieu 《Cell and tissue research》1987,248(1):201-205
Summary Cell nuclei containing progesterone receptor were identified immunohistochemically in the hypothalamus and forebrain of the domestic hen using an antiserum to the steroid binding B subunit (110 kDa) of chicken oviduct progesterone receptor and the avidin-biotin complex procedure. Cell nuclei containing progesterone receptor were widely distributed in the anterior, medial and basal hypothalamus with the highest density occurring in the lamina terminalis and the preoptic area. Abundant, though less intensely reacting progesterone receptor was present in cell nuclei in the tuberal infundibular area and in the internal zone of the median eminence. A large group of cell nuclei containing progesterone receptor occurred in the dorsal anterior hypothalamus between the anterior commissure and the lateral ventricle. This group of nuclei extended anteriorly into the telencephalon. A small number of cell nuclei containing progesterone receptor was also found in the ventral telencephalon in the region of the nucleus accumbens. 相似文献
143.
External pollen morphology of 39 species of West Indian Vernonias was examined by light and scanning electron microscopy in conjunction with a systematic revision of these species. There were three distinct types of pollen: Type A: subechinolophate, tricolporate grains with prominent spines; Type B: echinolophate, tricolporate with expanded germinal furrows and coincident polar muri; Type C: echinolophate, tricolporate grains with prominent polar lacunae. Pollen grains intermediate between the major types were found in several species. These same species had very distinct and atypical megamorphologies. In general, pollen types were found to correlate well with classification based on megamorphological characters, particularly at the infrageneric level, and to provide confirmation of subsectional assignments in the genus. 相似文献
144.
The multiple biological roles of the 3'-->5' exonuclease of Saccharomyces cerevisiae DNA polymerase delta require switching between the polymerase and exonuclease domains
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Jin YH Garg P Stith CM Al-Refai H Sterling JF Murray LJ Kunkel TA Resnick MA Burgers PM Gordenin DA 《Molecular and cellular biology》2005,25(1):461-471
Until recently, the only biological function attributed to the 3'-->5' exonuclease activity of DNA polymerases was proofreading of replication errors. Based on genetic and biochemical analysis of the 3'-->5' exonuclease of yeast DNA polymerase delta (Pol delta) we have discerned additional biological roles for this exonuclease in Okazaki fragment maturation and mismatch repair. We asked whether Pol delta exonuclease performs all these biological functions in association with the replicative complex or as an exonuclease separate from the replicating holoenzyme. We have identified yeast Pol delta mutants at Leu523 that are defective in processive DNA synthesis when the rate of misincorporation is high because of a deoxynucleoside triphosphate (dNTP) imbalance. Yet the mutants retain robust 3'-->5' exonuclease activity. Based on biochemical studies, the mutant enzymes appear to be impaired in switching of the nascent 3' end between the polymerase and the exonuclease sites, resulting in severely impaired biological functions. Mutation rates and spectra and synergistic interactions of the pol3-L523X mutations with msh2, exo1, and rad27/fen1 defects were indistinguishable from those observed with previously studied exonuclease-defective mutants of the Pol delta. We conclude that the three biological functions of the 3'-->5' exonuclease addressed in this study are performed intramolecularly within the replicating holoenzyme. 相似文献
145.
146.
Wilson-Ashworth HA Judd AM Law RM Freestone BD Taylor S Mizukawa MK Cromar KR Sudweeks S Bell JD 《The Journal of membrane biology》2004,200(1):25-33
Palmitoyl-lysophosphatidylcholine promotes a transient calcium influx in lymphoma cells. Previously, it was observed that this influx was accompanied by a temporary increase in propidium iodide permeability that appeared linked to calcium entry. Those studies demonstrated that cobalt or nickel could block the response to lysophosphatidylcholine and raised the question of whether the calcium conductance involved specific channels. This communication describes a series of experiments to address that issue. The time dependence and structural specificity of the responses to lysophosphatidylcholine reinforced the hypothesis of a specific channel or transporter. Nevertheless, observations using patch clamp or calcium channel blockers suggested that this “channel” does not involve proteins. Alternative protein-mediated mechanisms such as indirect involvement of the sodium-calcium exchanger and the sodium-potassium ATPase were also excluded. Experiments with extracellular and intracellular calcium chelators suggested a common route of entry for calcium and propidium iodide. More directly, the ability of lysophosphatidylcholine to produce cobalt-sensitive permeability to propidium iodide was reproduced in protein-free artificial membranes. Finally, the transient nature of the calcium time course was rationalized quantitatively by the kinetics of lysophosphatidylcholine metabolism. These results suggest that physiological concentrations of lysophosphatidylcholine can directly produce membrane pores that mimic some of the properties of specific protein channels.This revised version was published online in June 2005 with a corrected cover date. 相似文献
147.
Cystic fibrosis transmembrane conductance regulator in human and mouse red blood cell membranes and its interaction with ecto-apyrase 总被引:1,自引:0,他引:1
Sterling KM Shah S Kim RJ Johnston NI Salikhova AY Abraham EH 《Journal of cellular biochemistry》2004,91(6):1174-1182
Elevated blood ATP and increased red blood cell (RBC) ATP transport is associated with cystic fibrosis (CF). In this report, we demonstrate the presence of the wild-type and the DeltaF508 mutant form of the CF transmembrane conductance regulator protein in RBC membranes and its putative interaction with ecto-apyrase, an ATP hydrolyzing enzyme also present in the RBC membrane. RBC membranes of control and DeltaF508 individuals and of wild-type and CF transmembrane conductance regulator-knockout mice were examined by immunoblot using several antibodies directed against different epitopes of this protein. These experiments indicated that human RBC membranes contain comparable amounts of the wild-type CF transmembrane conductance regulator protein and the DeltaF508 mutant form of the protein, respectively. CF transmembrane conductance regulator protein was also detected in wild-type mouse RBC membranes but not in the gene knockout mouse RBC membranes. Antibodies directed against ecto-apyrase co-immunoprecipitated CF transmembrane conductance regulator protein of human RBC membranes indicating a physical interaction between these two membrane proteins consistent with ATP transport and extracellular hydrolysis. We conclude that RBCs are a significant repository of CF transmembrane conductance regulator protein and should provide a novel system for evaluating its expression and function. 相似文献
148.
Parker WG Irmis RB Nesbitt SJ Martz JW Browne LS 《Proceedings. Biological sciences / The Royal Society》2005,272(1566):963-969
A new discovery of skeletons of Revueltosaurus callenderi from the Upper Triassic Chinle Formation of Petrified Forest National Park, Arizona clearly shows that Revueltosaurus is not an ornithischian dinosaur as previously supposed. Features such as the presence of a postfrontal, crocodile-normal ankle and paramedian osteoderms with anterior bars place R. callenderi within the Pseudosuchia, closer to crocodylomorphs than to dinosaurs. Therefore, dental characters previously used to place Revueltosaurus within the Ornithischia evolved convergently among other archosaur taxa, and cannot be used to diagnose ornithischian dinosaur teeth. As a result, all other putative North American Late Triassic ornithischians, which are all based exclusively on teeth, are cast into doubt. The only reasonably well-confirmed Late Triassic ornithischians worldwide are Pisanosaurus mertii and an unnamed heterodontosaurid from Argentina. This considerably changes the understanding of early dinosaur diversity, distribution and evolution in the Late Triassic. 相似文献
149.
Clarence Sterling 《American journal of botany》1964,51(4):354-360
A survey of species of the prunoid genera, Maddenia and Pygeum, and of the genus Osmaronia has been made. The ovules of all are pendent, campylotropous, and epitropic. In the prunoids, the ovular supply is intimately connected with a central vascular plexus in the base of the carpel; that plexus is absent from Osmaronia. The prunoid carpels are marked by an extensive degree of fusion among the ovular and wing bundles, by fusion of the sutural margins, by fusion of the 2 integuments of the ovule to a single massive one, and by the presence of 3 or 5 well-developed bundles in the base. The carpel of Osmaronia also has a strongly fused bipartite ovular supply, separate bundles of which, however, become very much attenuated before reaching the funiculus; it has independent ovular and wing bundles, completely separate carpellary margins, 2 clearly separate integuments in the ovule, and 6 distinctive bundles in the carpel base. At the funiculus, the wing bundle of Osmaronia is connected with the adjoining weak ovular bundle by a well-developed vascular branch. Various particularities in the morphology of Osmaronia lend support to its segregation into a unique tribe, the Osmaronieae of Rydberg. 相似文献
150.
Slime a plasmodioid variant ofNeurospora crassa 总被引:1,自引:0,他引:1
Sterling Emerson 《Genetica》1964,34(1):162-182
The slime variant of Neurospora is unique among the higher Fungi in growing on an agar surface by plasmodium-like outflows which are devoid of cell walls, and in which cells from older parts of an agar colony, and those in liquid culture, have very deficient cell walls. Heterocaryon studies indicate that the nucleus determines the slime phenotype. Genetic studies show that three independently inherited characters are essential to but insufficient for the slime phenotype. Some, but not all isolates with all three characteristics give rise to vegetatively derived isolates with stable slime phenotypes.Supported in part by grant G-6174 from the National Science Foundation, and in part by grant GM-06965 from the National Institutes of Health, U.S. Public Health Service. 相似文献