Gamma-ray irradiation as a pretreatment for the enzymatic hydrolysis of cellulose

Summary The susceptibility of cellulose to enzymatic hydrolysis can be significantly affected through pretreatment by means of gamma-ray radiation. Experiments were carried out to investigate the effects of this radiation on enzymatic hydrolysis and on the two major structural features of cellulose that most influence hydrolysis, namely, specific surface area and crystallinity.D. H. Beardmore is currently with Phillips Petroleum Company, Bartlesville, OK 74004, U.S.A.     

Up-regulation of granulocyte-macrophage colony-stimulating factor (GM-CSF) receptors in murine peritoneal exudate macrophages by both GM-CSF and IL-3.

Murine peritoneal exudate macrophages (PEM) display multiple CSF receptors. In this study, the expression of granulocyte-macrophage (GM)-CSF receptors in PEM was studied. PEM displayed over 5000 single type, high affinity GM-CSF receptors/cell with a Kd = 38 to 42 pM and an apparent molecular mass of 86,000 Da. Treatment of PEM with low, but not high, concentrations of recombinant murine (rMu) GM-CSF continuously for 24 h resulted in a marked up-regulation of GM-CSF receptors in PEM. A similar up-regulation of GM-CSF receptors also was detected in PEM cultures treated with rMuIL-3 (1-100 ng/ml) for 24 h or longer, regardless the doses of rMuIL-3 added in this case. Scatchard analysis of equilibrium binding showed that the enhanced binding activities in both cases were due to an increase in total number of GM-CSF receptors rather than changes in receptor affinity. Contrariwise, treatment with recombinant human macrophage-CSF (greater than 100-1000 ng/ml) partially inhibited the expression of GM-CSF receptors in PEM. Removal of rMuGM-CSF from culture medium 24 h after treatment led to a further up-regulation of GM-CSF receptors over a 4 to 24-h period, depending on the doses of initial treatment. On the other hand, removal of rMuIL-3 from culture medium after prolonged treatment did not result in further increase in GM-CSF receptors. The protein synthesis inhibitor cycloheximide abrogated GM-CSF receptor up-regulation induced by both rMuIL-3 and rMuGM-CSF, whereas actinomycin D inhibited only the second (8-24 h) phase of GM-CSF receptor up-regulation induced by exposure to high concentrations rMuGM-CSF (10 ng/ml). These findings suggest that rMuGM-CSF and rMuIL-3 up-regulate GM-CSF receptors in PEM in part through similar or identical metabolic pathways and provide further evidence of a close linkage between IL-3 and GM-CSF receptors.     

Characterization of the Ni-Fe-C complex formed by reaction of carbon monoxide with the carbon monoxide dehydrogenase from Clostridium thermoaceticum by Q-band ENDOR.

Q-Band ENDOR studies on carbon monoxide dehydrogenase (CODH) from the acetogenic bacterium Clostridium thermoaceticum provided unambiguous evidence that the reaction of CO with CODH produces a novel metal center that includes at least one nickel, at least three iron sites, and the carbon of one CO. The 57Fe hyperfine couplings determined by ENDOR are similar to the values used in simulation of the M?ssbauer spectra [Lindahl et al. (1989) J. Biol. Chem. 265, 3880-3888]. EPR simulation using these AFe values is equally good for a 4Fe or a 3Fe center. The 13C ENDOR data are consistent with the binding of a carbon atom to either the Ni or the Fe component of the spin-coupled cluster. The 13C hyperfine couplings are similar to those determined earlier for the C0-bound form of the H cluster of the Clostridium pasteurianum hydrogenase, proposed to be the active site of hydrogen activation [Telser et al. (1987) J. Biol. Chem. 262, 6589-5694]. The 61 Ni ENDOR data are the first nickel ENDOR recorded for an enzyme. The EPR simulation using the ENDOR-derived hyperfine values for 61Ni is consistent with a single nickel site in the Ni-Fe-C complex. On the basis of our results and the M?ssbauer data [Lindahl et al. (1989) J. Biol. Chem. 265, 3880-3888], we propose the stoichiometry of the components of the Ni-Fe-C complex to be Ni1Fe3-4S greater than or equal to 4C1, with four acid-labile sulfides.     

Bubble flow in the downflow section of an airlift tower

Characterization of the two-phase flow in the downflow section of the airlift tower is necessary for accurate modeling of the airlift tower. A Split-cylinder airlift tower was investigated for superficial gas velocities ranging from 0.0683 to 0.3315 m/sec for an air–water system. Statistical cross-covariance techniques were used to yield velocities, void fractions, and flow rates corresponding to upward and downward components of bubble flow in the downflow section of the airlift tower. From these results the fraction of incoming air entrained in the downflow section was determined as a function of superficial gas velocity and position.     

Effects of temperature on diphosphopyridine nucleotide-linked isocitrate dehydrogenase from bovine heart. Aspects of the kinetics, stability, and quarternary structure of the enzyme.

A temperature-dependent conformational change of the active DPN-linked isocitrate dehydrogenase was observed. When initial reaction kinetic data were examined between 35 and 5 degrees, the Hill number (n) varied from 2 at higher to n approaching unity at lower temperatures, with an inflection point at 17 degrees. The presence of manganous isocitrate in the incubation media shifted the transition temperature for enzyme inactivation by 5,5'-dithiobis(2-nitrobenzoate) from 8-16 degrees. These temperature-dependent transitions were paralleled by progressive changes in sedimentation velocities from s20, w of 10.4 at 25 degrees to 7.3 at 10 degrees as measured by active band centrifugation. The linear Arrhenius plot for apparent V max and the constancy of S0.5 for the substrate manganous isocitrate between 35 and 5 degrees suggest that this temperature-dependent conformational change may not be solely related to manganous isocitrate. Further indications of equilibria between different species of enzyme in solution and effects of substrates and cofactors on conformation came from studies of specific activity of enzyme diluted into buffers at 3 and 25 degrees. Dilution to concentrations between 10 and 25 mum enzyme resulted in relatively rapid protein concentration-dependent inactivation which could be prevented and fully reversed by manganous isocitrate. No further substantial inactivation was found subsequent to this phase at 25 degrees. Lowering the temperature of the dilution buffer to 3 degrees favored formation of enzyme species exhibiting a further time and pH-dependent loss of activity which became independent of protein concentration below 7 mum enzyme. The rate of cold inactivation was reduced by raising the ionic strength of the buffer and its progress could be arrested by manganous isocitrate; however, the substrate did not restore the original activity.     

LGR5 regulates osteogenic differentiation of human thoracic ligamentum flavum cells by Wnt signalling pathway

Thoracic ossification of the ligamentum flavum (TOLF) is ectopic ossification of the spinal ligaments. Histologically, the development of TOLF can be described as the process of endochondral ossification. However, the underlying aetiology has not been completely clarified. In this investigation, the gene expression profile associated with leucine‐rich repeat‐containing G‐protein‐coupled receptors (LGR) and Wnt signalling pathway in the thoracic ligamentum flavum cells (TLFCs) of different ossification stages was analysed via RNA sequencing. We further confirmed the significant differences in the related gene expression profile by Gene Ontology (GO) enrichment analysis. LGR5 was first identified in primary human TLFCs during osteogenic differentiation. To evaluate the effect of LGR5 on osteogenic differentiation, LGR5 has been knocked down and overexpressed in human TLFCs. We observed that the knockdown of LGR5 inhibited the activity of Wnt signalling and attenuated the potential osteogenic differentiation of TLFCs, while overexpression of LGR5 activated the Wnt signalling pathway and increased osteogenic differentiation. Our results provide important evidence for the potent positive mediatory effects of LGR5 on osteogenesis by enhancing the Wnt signalling pathway in TOLF.     

转录因子在植物干旱应激中的功能研究进展

转录因子是一种多功能蛋白,在感知应激信号、应答相应应激基因表达及传导应激信号中起着关键作用。干旱是影响植物生长发育的主要非生物胁迫之一。为了适应干旱环境,植物发展了复杂的分子机制,其中转录因子可同时控制多种途径调控干旱应激,是操纵调控和应激响应途径的有力工具。近年来,越来越多的植物转录因子的功能被阐明,了解转录因子在干旱应激的功能,对植物的工程抗旱有重要的实践意义。综述转录因子在植物干旱应激中的功能研究进展,以期为今后转录因子的研究和利用提供理论依据,培育具有较强抗旱能力的植物。     

Differential effect of three-repeat and four-repeat tau on mitochondrial axonal transport

Tau protein is present in six different splice forms in the human brain and interacts with microtubules via either 3 or 4 microtubule binding repeats. An increased ratio of 3 repeat to 4 repeat isoforms is associated with neurodegeneration in inherited forms of frontotemporal dementia. Tau over-expression diminishes axonal transport in several systems, but differential effects of 3 repeat and 4 repeat isoforms have not been studied. We examined the effects of tau on mitochondrial transport and found that both 3 repeat and 4 repeat tau change normal mitochondrial distribution within the cell body and reduce mitochondrial localization to axons; 4 repeat tau has a greater effect than 3 repeat tau. Further, we observed that the 3 repeat and 4 repeat tau cause different alterations in retrograde and anterograde transport dynamics with 3 repeat tau having a slightly stronger effect on axon transport dynamics. Our results indicate that tau-induced changes in axonal transport may be an underlying theme in neurodegenerative diseases associated with isoform specific changes in tau's interaction with microtubules.