新疆绿蟾蜍的染色体组型初步研究

近年来,有关两栖类的染色体组型已有不少报道。无尾两栖类中蜍蟾属(Bufo)的染色体数目分为两类:2n=22和2n=20(Blain,1972)。我们对采自新疆4个地区的绿蟾蜍进行了染色体组型分析,发现其二倍体细胞染色体数均为44,是四倍体。现将我们的初步研究报道如下。     

Influence of dietary fiber on xylanolytic and cellulolytic bacteria of adult pigs.

Xylanolytic and cellulolytic bacteria were enumerated over an 86-day period from fecal samples of 10 8-month-old gilts that were fed either a control or a 40% alfalfa meal (high-fiber) diet. Fecal samples were collected from all pigs on days 0, 3, 5, 12, 25, 37, 58, and 86. Overall, the numbers of xylanolytic bacteria producing greater than 5-mm-diameter zones of clearing on 0.24% xylan roll tube medium after 24 to 36 h of incubation were 1.6 X 10(8) and 4.2 X 10(8)/g (dry weight) of feces for the control pigs and those fed the high-fiber diet, respectively. After 1 week of incubation, a large number of smaller zones of clearing (1 to 2 mm) appeared. Besides Bacteroides succinogenes and Ruminococcus flavefaciens, which produced faint zones of clearing in xylan roll tubes, three strains which closely resembled B. ruminicola hydrolyzed and used xylan for growth. The overall numbers of cellulolytic bacteria producing zones of clearing in 0.5% agar roll tube medium were 0.36 X 10(8) and 4.1 X 10(8)/g for the control pigs and those fed the high-fiber diet, respectively. B. succinogenes was the predominant cellulolytic isolate from both groups of pigs, and R. flavefaciens was found in a ratio of approximately 1 to 15 with B. succinogenes. Degradation of xylan and cellulose, measured by in vitro dry matter disappearance after inoculation with fecal samples, was significantly greater for pigs fed the high-fiber diet than that for the controls. These data suggest that the number of fibrolytic microorganisms and their activity in the large intestine of the adult pig can be increased by feeding pigs high-alfalfa-fiber diets and that these organisms are similar to those found in the rumen.     

Lipopeptides of the N-terminus of Escherichia coli lipoprotein: synthesis, mitogenicity and properties in monolayer experiments

The N-terminal part of the lipoprotein from the outer membrane of Escherichia coli, tripalmitoyl-S-glyceryl-L-Cys-Ser and analogs with longer sequences, are polyclonal activators for B-lymphocytes. Triple-chain lipopeptides also constitute efficient low-molecular-weight carrier/adjuvant systems, which can be linked to antigens to yield immunogens for antibody production without further additives. This is the first report of monolayer experiments with chemically well defined, synthetic lipopeptide mitogens with the composition of the N-terminus of an important bacterial membrane protein. Various derivatives of the lipoprotein N-terminus were synthesized. These lipopeptides differed in the length of the peptide moiety, the number of fatty acid residues, and protective groups. In order to obtain the surface areas for the lipopeptides in isotherms and hysteresis isotherms, monolayer experiments with a computer-controlled film balance were performed. To get some information about the interaction of these compounds with typical membrane lipids mixed monolayers were formed from triple-chain lipopeptides with dipalmitoylphosphatidylcholine and cholesterol. A comparison of the mitogenic response of the compounds was made in an in vitro system with B-lymphocytes from Balb/c mice.     

人体单臂间歇运动对发汗调定点的影响

本工作系在微小气候相对恒定条件下,对10名健康男青年每人进行四项实验。实验 Ⅰ 为测定双侧腿足浸入43℃水中,诱发左前臂屈侧显现定量汗点时的口腔温度(舌下)阈值,作为发汗调定点参考值(ToSSP);实验 Ⅱ 为 Ⅰ 附加右臂间歇轻负荷运动(77W)时测定 ToSSP,部分对象还记录了皮肤电反应;实验 Ⅲ、Ⅳ 为 Ⅰ、Ⅱ 均附加4.5m/s 气流(22—25℃)直吹头面部,再分别测定 ToSSP。实验 Ⅰ 与 Ⅱ 同体对照22人次,Ⅲ 与 Ⅳ 同体对照24人次。结果表明,实验 Ⅱ、Ⅳ 的 ToSSP 均值及其潜伏期均值分别较 Ⅰ、Ⅲ 者降低(P<0.01)或缩短(P<0.001);Ⅰ、Ⅱ间的 ToSSP 均值差、潜伏期均值差,分别与 Ⅲ、Ⅳ 之间者无显著差异(P>0.2);Ⅱ、Ⅳ 的ToSSP 均值各与其实验开始前的口温均值亦无明显差异(P>0.5)。此结果支持运动时体温调定点下降的论点,并提示在研究体温调定点活动时,以 ToSSP 为指标较用发汗速率为优越,因 ToSSP 不为许多干扰因素所影响。     

Effect of water activity on enzymatic synthesis of cephalexin

Summary In enzymatic synthesis of cephalexin (CEX) from 7-amino-3-deacetoxycephalosporanic acid (7-ADCA) and D--phenylglycine methyl ester (PGM) using an acylase fromXanthomonas citri, it was found that the synthetic activity and conversion yield were enhanced markedly by depressing the water activity (a _w ) of reaction system. This enhancement was probably resulted from the change of thermodynamic equilibrium and maximized at a range ofa _w from 0.96 to 0.97.     

Molecular dynamics of the alpha-helical epitope of a novel synthetic lipopeptide foot-and-mouth disease virus vaccine

A novel synthetic foot-and-mouth disease virus (FMDV) peptide vaccine consisting of a synthetic B-cell and macrophage activator covalently linked to an amphiphilic alpha-helical T-cell epitope was developed. The low molecular weight vaccine of 3400 daltons is composed of virus VP1 antigenic determinant and the immunologically active lipotripeptide tripalmitoyl-S-glyceryl-cysteinyl-seryl-serine (P3CSS) as built-in adjuvant. The vaccine, tripalmitoyl-S-glyceryl-cysteinyl-seryl-seryl-FMDV-VP1 (VP1 = serotype O1K 135-154) induces protection against homologous challenge and serotype-specific virus neutralizing antibodies in guinea pigs after single administration without further adjuvants or carriers. A P3CSS conjugate with the FMDV-VP1 segment 135-154 of strain O Wuppertal produced only poor cross-protection against challenge with O1K virus. The antigenic determinant VP1(135-154) is an amphiphilic alpha-helix, as shown by CD. Molecular dynamics simulations (MDS) carried out using the highly homologous alpha-helical alcohol dehydrogenase (ADH) segment H3 as starting conformation for VP1(138-149) suggest that the FMDV segment 138-149 may adopt alpha-helical conformation during binding to its T-cell receptor, and that the development of the system during MDS may be considered as the dissociation step of the complex.     

New mutations fts-36, lts-33, and ftsW clustered in the mra region of the Escherichia coli chromosome induce thermosensitive cell growth and division.

Three new mutants of Escherichia coli showing thermosensitive cell growth and division were isolated, and the mutations were mapped to the mra region at 2 min on the E. coli chromosome map distal to leuA. Two mutations were mapped closely upstream of ftsI (also called pbpB), in a region of 600 bases; the fts-36 mutant showed thermosensitive growth and formed filamentous cells at 42 degrees C, whereas the lts-33 mutant lysed at 42 degrees C without forming filamentous cells. The mutation in the third new thermosensitive, filament-forming mutant, named ftsW, was mapped between murF and murG. By isolation of these three mutants, about 90% of the 17-kilobase region from fts-36-lts-33 to envA could be filled with genes for cell division and growth, and the genes could be aligned.     

Identification of an amino acid substitution in the benA, beta-tubulin gene of Aspergillus nidulans that confers thiabendazole resistance and benomyl supersensitivity

We are using molecular genetic techniques to identify sites of interaction of beta-tubulin with benzimidizole anti-microtubule agents. We have developed a marker-rescue technique for cloning mutant alleles of the benA, beta-tubulin gene of Aspergillus nidulans and have used the technique to clone two mutant benA alleles, benA16 and benA19. These are the only A. nidulans alleles known to confer resistance to the benzimidazole antimicrotubule agent thiabendazole and supersensitivity to other benzimidazole antimicrotubule agents including benomyl and its active breakdown product, carbendazim. benA16 has been shown, moreover, to reduce thiabendazole binding to beta-tubulin. We have sequenced the two mutant alleles and have found that they carry different nucleotide changes that cause the same single amino acid substitution, valine for alanine at amino acid 165. Since thiabendazole and carbendazim differ at only one side chain, the R2 group, we conclude that the region around amino acid 165 is involved in the binding of the R2 group of benzimidazole antimicrotubule agents to beta-tubulin.