海枣曲霉β-半乳糖苷酶的提纯与性质

 通过过聚乙二醇6000-磷酸钾缓冲液双相分离、Sephadex G-100凝胶过滤、DEAE-Sephadex A-50离子交换层析、羟基磷灰石层析及SephadexG-100凝胶过滤等提纯步骤,从海枣曲霉(Aspergillus phoenicis)麦麸培养物抽提液中提纯得到凝胶电泳均一的β-半乳糖苷酶。该酶的最适pH为3.5—4.0,最适温度为60℃(反应15分钟),在pH5.0—8.5之间及60℃以下稳定。在65℃和70℃保温时失活50％的时间分别为27和2分钟。用SDS凝胶电泳法和梯度凝胶电泳法分别测得该酶的分子量为115,000和118,000。薄层凝胶等电聚焦法测得其等电点为pH4.6。     

Purified N-cadherin is a potent substrate for the rapid induction of neurite outgrowth

N-cadherin is the predominant mediator of calcium-dependent adhesion in the nervous system (Takeichi, M. 1988. Development (Camb.). 102: 639-655). Investigations using antibodies to block N-cadherin function (Bixby, J.L., R.L. Pratt, J. Lilien, and L.F. Reichardt. 1987. Proc. Natl. Acad. Sci. USA. 84:2555-2569; Bixby, J.L., J. Lilien, and L.F. Reichardt. 1988. J. Cell Biol. 107:353-362; Tomaselli, K.J., K.N. Neugebauer, J.L. Bixby, J. Lilien, and L.F. Reichardt. 1988. Neuron. 1:33-43) or transfection of the N-cadherin gene into heterologous cell lines (Matsunaga, M., K. Hatta, A. Nagafuchi, and M. Takeichi. 1988. Nature (Lond.). 334:62-64) have provided evidence that N-cadherin, alone or in combination with other molecules, can participate in the induction of neurite extension. We have developed an affinity purification procedure for the isolation of whole N-cadherin from chick brain and have used the isolated protein as a substrate for neurite outgrowth. N-cadherin promotes the rapid extension of neurites from chick ciliary ganglion neurons, which extend few or no neurites on adhesive but noninducing substrates such as polylysine, tissue culture plastic, and collagens. N-cadherin is extremely potent, more so than the L1 adhesion molecule, and comparable to the extracellular matrix protein laminin. Compared to laminin, however. N-cadherin promotes outgrowth from ciliary ganglion neurons extremely rapidly and with a distinct morphology. These results provide a direct demonstration that N-cadherin is sufficient to induce neurite outgrowth when substrate bound and suggest that the mechanism(s) involved may differ from that induced by laminin.     

Phosphorus concentration in barley (Hordeum vulgare L.) seed: Influence on seedling growth and dry matter production

The effect of phosphorus (P) concentration in barley seed on seedling growth has not been much investigated. Consequently, two experiments were conducted in the greenhouse to determine the effect of P concentration in barley seed (Hordeum vulgare L., cv. Empress) on the seedlings grown in sand-filled boxes receiving a culture solution without P. Seeds were selected with three P concentrations: high-P (113.0 mmol P kg⁻¹), medium-P (80.7 mmol P kg⁻¹) and low-P (54.9 mmol P kg⁻¹). At 21 days after sowing, the shoot and root yield or shoot height was the least with seedlings from low-P seed. In the other experiment, high-P and low-P seeds were wetted with distilled water or with a solution of 25.8 cmol L⁻¹ of NaH₂PO₄ for 24 h, and then grown for 31 days. Solution P had been imbibed by seeds whether low or high in native P, but only the imbibed P held by low native P seed benefited seedling dry matter accumulation and shoot elongation. The lack of benefit from seed-imbibed P on seedlings grown from high-P barley seed was associated with low recovery of the imbibed P in those seedlings.     

Generation of hydroxyl radical by crocidolite asbestos is proportional to surface [Fe3+].

Differences among fibrous silicates to effect injury in biological systems have been postulated to reflect oxidant generation by structural iron within the crystal lattice of amphiboles. Iron is also coordinated to the surface of all silicates in concentrations which depend on the density of acidic functional groups. We tested the hypothesis that oxidant generation by crocidolite is proportional to surface-complexed iron rather than variance in the lattice concentrations of this transition metal. Surface iron was quantified after its reduction to Fe2+ and chelation by citrate. Thiobarbituric acid (TBA) reactive products and dihydroxybenzoic acid products of salicylate were employed as indices of nonspecific oxidant and hydroxyl radical generation, respectively. Surface iron, TBA reactive products, and dihydroxybenzoic acid products all diminished after pretreatment of crocidolite with the metal chelator deferoxamine in concentrations varying from 0 to 250 mM. Inclusion of deferoxamine in the reaction mixture provided similar results of diminishing both TBA reactive products and dihydroxybenzoic acid generation. We conclude that oxidant generation by crocidolite is proportional to surface concentrations of iron which can be chelated using deferoxamine. The design of synthetic fibers without health effects after exposure will likely necessitate decreasing the number of surface acidic functional groups to diminish the capacity to complex iron (i.e., minimize the percentage SiO2).     

Parametric study of diethyl phthalate biodegradation

Summary The effects of temperature, dissolved oxygen, and other environmental parameters under both aerobic and anaerobic conditions were investigated using one aerobic and one facultative strain isolated from wastewater treatment plant sludge. Among other results, we found that low dissolved oxygen levels and low temperatures decreased the rate of DEP degradation and the growth rate, and that the facultative strain was much less affected by the lower DO concentrations than the aerobic strain.     

农业生态系统中新物种引进的初步探讨

在现有的农业生态系统中,引进某些新物种,往往可以使整个系统的功能发生变化。如果新物种引进得当,则可产生良好的效果,系统功能得以改善,效益提高;反之,则会造成人力、物力、财力的损失,削弱系统的功能,甚至可能遗患无穷。因此,对农业生态系统中