1．5t级农用运输车底盘与发动机匹配的综合研究

分析了目前１．５吨级农用运输车柴油机和底盘匹配不够合理的现状，综合研究了当柴油机给定后，优选传动系参数和给定底盘参数后，优选发动机参数，以达到最佳匹配的方法．     

Nucleotide-binding domains of human cystic fibrosis transmembrane conductance regulator: detailed sequence analysis and three-dimensional modeling of the heterodimer

The cystic fibrosis transmembrane conductance regulator (CFTR) protein is encoded by the gene that is defective in cystic fibrosis, the most common lethal inherited disease among the Caucasian population. CFTR belongs to the ABC transporter superfamily, whose members form macromolecular architectures composed of two membrane-spanning domains and two nucleotide-binding domains (NBDs). The experimental structures of NBDs from several ABC transporters have recently been solved, opening new avenues for understanding the structure/function relationships and the consequences of some disease-causing mutations of CFTR. Based on a detailed sequence/structure analysis, we propose here a three-dimensional model of the human CFTR NBD heterodimer. This model, which is in agreement with recent experimental data, highlights the specific features of the CFTR asymmetric active sites located at the interface between the two NBDs. Moreover, additional CFTR-specific features can be identified at the subunit interface, which may play critical roles in active site interdependence and are uncommon in other NBD dimers.Received 16 October 2003; received after revision 16 November 2003; accepted 21 November 2003     

A monosaccharide transporter is localized to sieve plate and plasmodesmal channel in developing apple fruit

Two major classes of plant sugar transporters, sucrose and monosaccharide transporters, may be localized to tonoplast or plasma membrane. The monosaccharide transporters may also be localized in plastid. However, whether these transporters reside in other subcellular compartments remains unclear. We recently detected in apple fruit a 52 kD plasma membrane-localized monosaccharide transporter, and showed that this transporter may be functional in phloem unloading in the fruit. In this paper, we report that this monosaccharide transporter is also localized to sieve plate and plasmodesmal channel in apple fruit. The amount of this sieve plate- and plasmodesma-associated transporter changes during fruit development. This amount of the transporter expression may be altered in the phloem sieve elements but not in the parenchyma cells by a photoassimilate deficiency applied by the shoot girdling treatment, suggesting that the monosaccharide transporter of the special sub-cellular localization may be of biological significance.     

成庄矿主井胶带机驱动控制系统的改进

分析了成庄矿主井胶带机驱动控制系统设备出现故障的原因,论述了驱动控制系统改进方案的确定原则,并详细介绍了改进方案。     

Multiple flavonoid-binding sites within multidrug resistance protein MRP1

Recombinant nucleotide-binding domains (NBDs) from human multidrug resistance protein MRP1 were overexpressed in bacteria and purified to measure their direct interaction with high-affinity flavonoids, and to evaluate a potential correlation with inhibition of MRP1-mediated transport activity and reversion of cellular multidrug resistance. Among different classes of flavonoids, dehydrosilybin exhibited the highest affinity for both NBDs, the binding to N-terminal NBD1 being prevented by ATP. Dehydrosilybin increased vanadate-induced 8-N₃-[-³²P]ADP trapping, indicating stimulation of ATPase activity. In contrast, dehydrosilybin strongly inhibited leukotriene C₄ (LTC₄) transport by membrane vesicles from MRP1-transfected cells, independently of reduced glutathione, and chemosensitized cell growth to vincristine. Hydrophobic C-isoprenylation of dehydrosilybin increased the binding affinity for NBD1, but outsite the ATP site, lowered the increase in vanadate-induced 8-N₃-[-³²P]ADP trapping, weakened inhibition of LTC₄ transport which became glutathione dependent, and induced some cross-resistance. The overall results indicate multiple binding sites for dehydrosilybin and its derivatives, on both cytosolic and transmembrane domains of MRP1.Received 1 May 2003; received after revision 18 June 2003; accepted 24 June 2003     

纳米中药——中药现代化的新途径

纳米中药是近年来迅速发展起来的前沿科技领域,与传统中药比较有其优势及特色.纳米中药的开发需要多学科的合作与研究,是传统中药走向国际化的方向,具有着广阔的前景.     

Purification of breast cancer resistance protein ABCG2 and role of arginine-482

Human ABCG2 was efficiently overexpressed in insect cell membranes, solubilized with 3-[(3-cholamidopropyl)dimethyl ammonio]-1-propanesulfonate, and purified through N-terminal hexahistidine tag. Its functionality was assessed by high vanadate-sensitive ATPase activity, and nucleotide-binding capacity. Interestingly, the R482T point mutation increased both maximal hydrolysis rate and affinity for MgATP, and lowered sensitivity to vanadate inhibition. Direct nucleotide binding, as monitored by quenching of intrinsic fluorescence, indicated a mutation-related preference for ATP over ADP. The R482T mutation only produced a limited change, if any, on the binding of drug substrates, indicating that methotrexate, on the one hand, and rhodamine 123 or doxorubicin, on the other hand, bound similarly to wild-type and mutant transporters whether or not they were subject to cellular transport. In addition, the characteristic inhibitors GF120918 and 6-prenylchrysin, which alter mitoxantrone efflux much better for wild-type than mutant ABCG2, bound similarly to purified ABCG2, while the highly-potent Ko143 bound in the nanomolar range also effective in inhibition of drug transport. All results indicate that the role of the arginine-482 mutation on substrate drug transport and inhibitor efficiency is not mediated by changes in drug binding. Received 10 April 2006; received after revision 22 May 2006; accepted 12 June 2006 A. Pozza and J. M. Perez-Victoria contributed equally to this work     

Conformational changes in a bacterial multidrug transporter are phosphatidylethanolamine-dependent

LmrP is an electrogenic H⁺/drug antiporter that extrudes a broad spectrum of antibiotics. Five carboxylic residues are implicated in drug binding (Asp142 and Glu327) and proton motive force-mediated restructuring (Asp68, Asp128 and Asp235). ATR-FTIR (Attenuated Total Reflection – Fourier Transform Infrared) and tryptophan quenching experiments revealed that phosphatidylethanolamine (PE) is required to generate the structural intermediates induced by ionization of carboxylic residues. Surprisingly, no ionization-induced conformational changes were detectable in the absence of PE, suggesting either that carboxylic acid residues do not ionize or that ionization does not lead to any conformational change. The mean pKa of carboxylic residues evaluated by ATR-FTIR spectroscopy was 6.5 for LmrP reconstituted in PE liposomes, whereas the pKa calculated in the absence of PE was 4.6. Considering that 16 of the 19 carboxylic residues are located in the extramembrane loops, the pKa values obtained in the absence and in the presence of PE suggest that the interaction of the loop acid residues with the membrane interface depends on the lipid composition. Received 23 January 2007; received after revision 2 April 2007; accepted 20 April 2007     

Spore germination

Despite being relatively insensitive to environmental insult, the spore is responsive to low concentrations of chemical germinants, which induce germination. The process of bacterial spore germination involves membrane permeability changes, ion fluxes and the activation of enzymes that degrade the outer layers of the spore. A number of components in the spore that are required for the germination response have been identified, including a spore-specific family of receptor proteins (the GerA family), an ion transporter and cortex lytic enzymes. The germinant traverses the outer layers of the spore and interacts with its receptor in the inner membrane to initiate the cascade of germination events, but the molecular details of this signal transduction process remain to be identified.