Regulation of cellulase synthesis in mycelial fungi: Participation of ATP and cyclic AMP

Summary ATP and cAMP in 4 strains of mycelial fungi were determined by luciferin-luciferase system and HPLC respectively. Cellulase synthesis was subject to the dual control of ATP and cAMP. No matter what carbon sourse was used, cellulase synthesis was repressed if intracellular ATP concentration was over 10^-7mg/ml. Exogenous cAMP could increase cellulase synthesis under depression conditions.     

Kinetics and mechanism of CO substitution of [η-CpFe(CO)3]PF6 with PPh3 in the presence of substituted pyridine N-oxide

The kinetics of substitution reactions of [η-CpFe(CO)₃]PF₆ with PPh₃ in the presence of R-PyOs have been studied. For all the R-PyOs (R = 4-OMe, 4-Me, 3,4-(CH)₄, 4-Ph, 3-Me, 2,3-(CH)₄, 2,6-Me₂, 2-Me), the reactions yeild the same product [η⁵-CpFe(CO)₂PPh₃]PF₆, according to a second-order rate law that is first order in concentrations of [η⁵-CpFe(CO)₃]PF₆ and of R-PyO but zero order in PPh₃ concentration. These results, along with the dependence of the reaction rate on the nature of R-PyO, are consistent with an associative mechanism. Activation parameters further support the bimmolecular nature of the reactions: ΔH^≠ = 13.4 ± 0.4 kcal mol⁻¹, ΔS^≠ = −19.1 ± 1.3 cal k⁻¹ mol⁻¹ for 4-PhPyO; ΔH^≠ = 12.3 ± 0.3 kcal mol⁻¹, ΔS^≠ = 24.7 ±1.0 cal K⁻¹ mol⁻¹ for 2-MePyO. For the various substituted pyridine N-oxides studied in this paper, the rates of reaction increase with the increasing electron-donating abilities of the substituents on the pyridine ring or N-oxide basicities, but decrease with increasing ¹⁷O chemical shifts of the N-oxides. Electronic and steric factors contributing to the reactivity of pyridine N-oxides have been quantitatively assessed.     

Caloric Restriction: Conservation of in Vivo Cellular Replicative Capacity Accompanies Life-Span Extension in Mice

In male mice of a long-lived hybrid strain (B6D2F1), long-term 40% caloric restriction (CR) extended both mean and maximum life spans by 36 and 20%, respectively, over that of ad libitum fed (AL) controls. Measurements of entry into S-phase were made in vivo of six different cell types in five different organs using 2-week exposures to BrdU. The labeling index (L.I.) in all organs studied was lower in young CR mice than in young AL fed mice. In most cases, the L.I. in AL mice fell to the levels of that in the CR mice by 13 months of age, and the two groups then remained so through old age. However, when the L.I. was measured in old CR mice which had been placed on the AL diet for a period of 4 weeks (this was termed refeeding (RF)), it was found to be above that of similar age AL or CR mice and almost at the level of young AL mice. This was still true, but to a lesser degree, in a repeat study using an 8-week period of RF. In a separate but parallel in vitro study (companion paper, this volume), the superiority of CR over AL for retention of cellular replication capacity was confirmed by clone size distribution measurements made in several cell types in mice of several age groups. These results indicate that: (1) the rate of cell replication in AL diet mice diminishes greatly by early middle age in all organ sites studied and then plateaus or declines much more slowly; (2) CR broadly preserves in vivo cellular replicative capacity but often requires the energy levels provided by a switch to AL feeding to demonstrate this late in life; (3) accordingly, the replicative deficit in AL fed mice appears to be cumulative and is significant only in old age. The mechanism(s) involved is yet to be discovered but may be related to, or even the same as, that which extends life spans in CR animals. Correspondingly, and with corroborative data from our in vitro companion study, (W. R. Pendergrass et al., 1995. Exp. Cell. Res. 217, 309-316), we suggest that cell populations sustain an accrual of biochemical damage or physiological alterations which increasingly limit their replicative capacity as the animal ages, and that CR reduces the accrual of this damage.     

新型表达载体 pEC34 试用于人 γ 干扰素基因的高表达

构建了一个新的双顺反子表达载体ｐＥＣ３４,它的第一个顺反子是已高表达的ｅｒａ基因的部分序列,并带有原核翻译增强子。当检测ｐＥＣ３４的可用性时,获得了人γ－干扰素的极高表达。目的蛋白占菌体总蛋白的８５．５％,诱导后经ＳＤＳ－ＰＡＧＥ分析,出现分子量为１５．５ｋＤａ左右的蛋白表达带。Ｗｅｓｔｅｒｎ ｂｌｏｔ结果证实为人γ－干扰素。无压力传代３０次表达质粒仍然稳定,表明ｐＥＣ３４可能用作真核蛋白质高表达     

GI双突变体GIK253RA198C的构建及其性质分析

以双引物法对葡萄糖异构酶（GI）基因进行定点突变,将突变体基因于大肠杆菌中表达,获得了GI双点突变体GIK253RA198C.研究K253R和A198C双点突变对GI的结构和性质的作用,结果表明GIK253RA198C的热稳定性明显下降,最适反应温度降低5℃.文章从结构和机制上解释了为何同是K253R突变,对SM33 GI和密苏里游动放线菌GI的热稳定性产生不同的影响,认为这是由于Lys253在两种GI结构的位置上存在微小差异,从而使引入的Arg对亚基间的相互作用产生了相反效应所引起.     

Melatonin and the pea aphid,Acyrthosiphon pisum

Pea aphids, Acyrthosiphon pisum, were fed on artificial diet containing various concentrations of melatonin. Under long-day conditions (16h light:8h dark) their progeny included males and virginoparous/oviparous (asexual/sexual) intermediate females, which normally occur only in short days or around critical night-length. Endogenous melatonin in pea aphids was measured by radioimmunoassay and verified by parallelism with a melatonin standard curve and by thin layer chromatography. However, melatonin titres showed large variations and although they tended to be higher during the scotophase than during the photophase they were not significantly different. The possibility of melatonin being involved in photoperiodism is discussed.     

Identification of Influenza C Virus Phosphoproteins

The HMV-II cells infected with influenza C virus were labeled with inorganic [³²P]phosphate to identify phosphorylated proteins. Analysis by radioimmunoprecipitation with antiviral serum or monoclonal antibodies revealed that three major structural proteins of the virus, hemagglutinin-esterase (HE), nucleoprotein (NP), and matrix protein (M1) are all phosphorylated in both infected cells and virions. It was also observed that, in the presence of trypsin (10 μg/ml), the unphosphorylated form of the HE glycoprotein was cleaved efficiently whereas the phosphorylated form was not, raising the possibility that phosphorylation of HE may influence its susceptibility to degradation by proteolytic enzymes.     

阳离子诱导大叶藻叶绿体膜中激发能在PSⅡ和PSⅠ之间分配变化的机理(英文)

用Ｃａ２＋ 和胰酶处理大叶藻（Ｚｏｓｔｅｒａ ｍ ａｒｉｎａ）叶绿体膜研究了其类囊体膜多肽成分与Ｍｇ２＋ 诱导其Ｃｈｌａ荧光和类囊体膜表面电荷变化之间的相互关系,观察到：１．在正常的叶绿体膜中,Ｍｇ２＋ 诱导ＰＳⅡ荧光强度的增高与其诱导类囊体膜表面电荷密度的降低密切相关;２．用Ｃａ２＋ 处理这种叶绿体膜,除去类囊体膜表面的３２～３４ ｋＤ多肽对Ｍｇ２＋ 诱导的上述现象无影响;３．如果用胰酶消化Ｃａ２＋ 处理过的叶绿体膜,进一步除去膜表面的２６ ｋＤ多肽,Ｍｇ２＋诱导的这些现象则全部消失。这些实验结果清楚地表明,在大叶藻的叶绿体膜中,类囊体膜表面的２６ ｋＤ 多肽是阳离子诱导这两种相关现象的特异性作用部位。对阳离子调节激发能在ＰＳⅡ和ＰＳⅠ之间分配的机理进行了讨论