大剂量~(60)Co照射后存活小鼠造血干细胞阈值的测定

本文应用CFU_s的剂量-存活曲线和干细胞移植后受体存活率测定法,摸清了F_1小鼠在临界死亡剂量—8.5 Gy γ-线照射后,存活的造血干细胞数量只有照前的1×10~(-4),约为20个左右的CFU_s或200个左右的HSC。因此,用造血干细胞计数可以作为估计辐射剂量和放射病早期诊断的敏感检测指标。这一细胞阈值的测定,为一些疾病的骨髓输注或骨髓移植治疗时的细胞数量提供了重要的依据。     

Evolutionary Theory and the Social uses of Biology

Stephen Jay Gould is rightly remembered for many different kinds of contributions to our intellectual life. I focus on his criticisms of uses of evolutionary ideas to defend inegalitarian doctrines and on his attempts to expand the framework of Darwinian evolutionary theory. I argue that his important successes in the former sphere are applications of the idea of local critique, grounded in careful attention to the details of the inegalitarian proposals. As he became more concerned with the second project, Gould was inclined to suggest that the abuses of evolutionary ideas rested on an insufficiently expanded Darwinism. I suggest that what is valuable in Gould's contribution to general evolutionary theory is the original claim about punctuated equilibrium (advanced, with Niles Eldredge in1972), and the careful defense of that claim through the accumulation of paleontological evidence. I try to show that the more ambitious program of a hierarchical expansion of neo-Darwinism is misguided, and that the endeavor to go beyond local critique fails.     

Phenological olive chilling requirements in Umbria (Italy) and Andalusia (Spain)

Phenological observations in olive tree (Olea europaea L.), on the first reproductive phase (budburst) and the winter chilling temperatures required for its onset, were analysed over a 4-year period (1998 - 2001). Research was carried out on two different cultivars growing in two Mediterranean olive-growing areas: 'Ascolana' in central Italy and 'Picudo' in southern Spain. The two main objectives of the study were: (1) to evaluate the different amounts of winter chilling, and their relationship with the budburst dates in outdoor olive plantations; and (2) to test the validity in the study areas of two chilling calculation methods, the Aron and the Utah method. Results show that for the Spanish cultivar the average chilling requirement of 997 h was approximately half of that recorded for the Italian cultivar (1848 h). Also, the year-to-year variability in chilling accumulation and the reproductive development date was observed to be higher in the Spanish area than in the Italian one, indicating a more consistent and predictable winter chilling response in the latter. As regards the validity of the methods, the Aron method seems to be more appropriate for use in warmer places, since it yielded better results in the Spanish site.     

Molecular Basis of Substrate Polyspecificity of the Candida albicans Mdr1p Multidrug/H+ Antiporter

The molecular basis of polyspecificity of Mdr1p, a major drug/H⁺ antiporter of Candida albicans, is not elucidated. We have probed the nature of the drug-binding pocket by performing systematic mutagenesis of the 12 transmembrane segments. Replacement of the 252 amino acid residues with alanine or glycine yielded 2/3 neutral mutations while 1/3 led to the complete or selective loss of resistance to drugs or substrates transported by the pump. Using the GlpT-based 3D–model of Mdr1p, we roughly categorized these critical residues depending on their type and localization, 1°/ main structural impact (“S” group), 2°/ exposure to the lipid interface (“L” group), 3°/ buried but not facing the main central pocket, inferred as critical for the overall H⁺/drug antiport mechanism (“M” group) and finally 4°/ buried and facing the main central pocket (“B” group). Among “B” category, 13 residues were essential for the large majority of drugs/substrates, while 5 residues were much substrate-specific, suggesting a role in governing polyspecificity (P group). 3D superposition of the substrate-specific MFS Glut1 and XylE with the MDR substrate-polyspecific MdfA and Mdr1p revealed that the B group forms a common substrate interaction core while the P group is only found in the 2 MDR MFS transporters, distributed into 3 areas around the B core. This specific pattern has let us to propose that the structural basis for polyspecificity of MDR MFS transporters is the extended capacity brought by residues located at the periphery of a binding core to accomodate compounds differing in size and type.     

Biometrical analysis reveals major differences between the two subspecies of the European rabbit

The climatic oscillations that have occurred in the last few million years have strongly affected species distribution ranges. Highly divergent genetic lineages arose, some of which correspond to recognized subspecies that currently occupy small geographical areas. Understanding the implications of the genetic differences between these subspecies is crucial for proper conservation of Evolutionarily Significant Units. We use the two European rabbit subspecies, Oryctolagus cuniculus cuniculus and O. c. algirus, in the Iberian Peninsula as a model to investigate the repercussions at the biometric level of their largely recognized genetic differentiation. To accomplish this we analysed the ear and hind foot length, and the body mass of 999 adult rabbits from 27 locations across the distribution range of both subspecies in their native range, the Iberian Peninsula. Our results show biometric differences between the two subspecies, also explained by geographical location and sex, O. c. algirus being lighter and having shorter ear and hind foot lengths. We examine these findings under an evolutionary framework, and discuss their implications for current conservation efforts. Future research should focus on the ecological implications of these biometric differences, namely potential different habitat use and anti‐predatory strategies in the species' native range.     

Kinetic study of the cellobiase activity of Trichoderma reesei cellulase complex at high substrate concentrations

At high cellobiose concentrations, the cellobiase activity of a Trichoderma reesei cellulase preparation does not follow Michaelis–Menten kinetics and shows substrate inhibition. Several rate equations were fitted to the initial rate-cellobiose concentration data. The best fit is obtained for a rate equation corresponding to partial substrate inhibition of cellobiase. In this case, the K_m, V_max and K_I values obtained are 1.1 mM, 16 IU ml^–1 and 26 mM, respectively.     

Insulin downregulates neonatal brain insulin receptors

Using cell cultures rich in renal juxtaglomerular cells we found that a change of the intracellular c-AMP concentration is not a prerequisite for an alteration of the renin secretion rate. Modulators of renin secretion including activators of the adenylate cyclase, however, altered the calcium permeability of the cellular plasma membrane in a way that stimulators of renin secretion lowered the calcium permeability and vice versa. Our results suggest that renin secretion is controlled by the intracellular calcium concentration and not by c-AMP. We postulate that modulators of renin secretion act by changing the calcium permeability of the cell membrane.     

Utilization of carbohydrates content of paper tube residuals for ethanol production

Paper tube residual was utilized as a raw material for ethanol production. The effects of two pretreatment methods namely dilute acid steam explosion (DASE) and concentrate phosphoric acid (CPA) on enzymatic hydrolysis and SSF were studied. Cellulose, lignin, glue (PVA), and xylan were the main components of paper tube accounting for 52%, 20%, 9% and 7% of dry matter, respectively. Presence of PVA delayed the growth of yeast cells but showed no effect on ultimate yield of ethanol. Higher cellulase concentration as well as pretreatments increased hydrolysis rate and ultimate yield of ethanol. Enzymatic hydrolysis of native paper tube for 72 h resulted in 49% of theoretical glucose conversion while pretreatments by DASE and CPA increased this value to 67% and 93%, respectively. The best result of SSF process was from the CPA-pretreated paper tubes with an ethanol yield of 0.42 g/g after 48 h. Under optimal condition, 308 ml ethanol per kg paper tube could be produced.     

固定化纤维二糖酶的研究

黑曲霉 (AspergillusnigerLORRE 0 12 )的孢子中富含纤维二糖酶 ,将这些孢子用海藻酸钙凝胶包埋后 ,可以方便有效地固定纤维二糖酶。固定化后的纤维二糖酶性能稳定 ,半衰期为 38d ,耐热性和适宜的pH范围均比固定化前有所增加 ,其Km 和Vmax值分别为 6 .0 1mmol L和 7.0 6mmol (min·L)。利用固定化纤维二糖酶重复分批酶解10g L的纤维二糖 ,连续 10批的酶解得率均可保持在 97%以上 ;采用连续酶解工艺 ,当稀释率为 0 .4h- 1 ,酶解得率可达 98.5 %。玉米芯经稀酸预处理后 ,其纤维残渣用里氏木霉 (Trichodermareesei)纤维素酶降解 ,酶解得率为6 9.5 % ;通过固定化纤维二糖酶的进一步作用 ,上述水解液中因纤维二糖积累所造成的反馈抑制作用得以消除 ,酶解得率提高到 84.2 % ,还原糖中葡萄糖的比例由 5 3 .6 %升至 89.5 % ,该研究结果在纤维原料酶水解工艺中具有良好的应用前景。