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用Aedans标记肌动蛋白单体G-Actin上Cys374残基作为探针,研究了稀土离子Ce~(3+)与G-Actin的结合及引起的微构象变化。Ce~(3+)在低浓度(Ce~(3+)/Actin摩尔比<1)和Ca~(2+)竞争G-Actin上二价离子的高亲合位点。Ce~(3+)取代Ca~(2+)引起Aedans荧光强度增强与Mg~(2+)取代Ca~(2+)的结果相同。Ce~(3+)/Actin>l则导致Aedans荧光强度下降。说明Ce~(3+)在高低两种浓度条件下结合的位点及对Cvs374的微构象的影响不同。时间分辩测得的Aedans荧光寿命也支持这一结论。CD谱结果表明Ce~(3+)/Actin<0.4,Actin的二级结构增加,大于0.4又导致其失去。Ce~(3+)-Actin在有/无游离ATP时用聚合液诱导的聚合结果表明,无游离ATP时,极低浓度Ce~(3+)促进聚合,高浓度虽有促进但有所减弱;有游离ATP时,Ce~(3+)/Actin在实验范围内促进聚合。 相似文献
55.
The Role of Pea Chloroplast [alpha]-Glucosidase in Transitory Starch Degradation 总被引:2,自引:1,他引:1 下载免费PDF全文
Pea chloroplastic [alpha]-glucosidase (EC 3.2.1.20) involved in transitory starch degradation was purified to apparent homogeneity by ion exchange, reactive dye, hydroxylapatite, hydrophobic interaction, and gel filtration column chromatography. The native molecular mass and the subunit molecular mass were about 49.1 and 24.4 kD, respectively, suggesting that the enzyme is a homodimer. The enzyme had a Km of 7.18 mM for maltose. The enzyme's maximal activity at pH 7.0 and stability at pH 6.5 are compatible with the diurnal oscillations of the chloroplastic stromal pH and transitory starch accumulation. This pH modulation of the [alpha]-glucosidase's activity and stability is the only mechanism known to regulate starch degradative enzymes in leaves. Although the enzyme was specific for the [alpha]-D-glucose in the nonreducing end as the glycon, the aglycon moieties could be composed of a variety of groups. However, the hydrolysis rate was greatly influenced by the aglycon residues. Also, the enzyme could hydrolyze glucans in which carbon 1 of the glycon was linked to different carbon positions of the penultimate glucose residue. The ability of the [alpha]-glucosidase to hydrolyze [alpha]-1,2- and [alpha]-1,3-glucosidic bonds may be vital if these bonds exist in starch granules because they would be barriers to other starch degradative enzymes. This purified pea chloroplastic [alpha]-glucosidase was demonstrated to initiate attacks on native transitory chloroplastic starch granules. 相似文献
56.
The structure and function of p55PIK reveal a new regulatory subunit for phosphatidylinositol 3-kinase. 总被引:8,自引:2,他引:6 下载免费PDF全文
S Pons T Asano E Glasheen M Miralpeix Y Zhang T L Fisher M G Myers Jr X J Sun M F White 《Molecular and cellular biology》1995,15(8):4453-4465
Phosphatidylinositol 3-kinase (PI-3 kinase) is implicated in the regulation of diverse cellular processes, including insulin-stimulated glucose transport. PI-3 kinase is composed of a 110-kDa catalytic subunit and an 85-kDa regulatory subunit. Here, we describe p55PIK, a new regulatory subunit that was isolated by screening expression libraries with tyrosine-phosphorylated insulin receptor substrate 1 (IRS-1). p55PIK is composed of a unique 30-residue NH2 terminus followed by a proline-rich motif and two Src homology 2 (SH2) domains with significant sequence identify to those in p85. p55PIK mRNA is expressed early during development, remains abundant in adult mouse brain and testis tissue, and is detectable in adult adipocytes and heart and kidney tissues. p55PIK forms a stable complex with p110, and it associates with IRS-1 during insulin stimulation. Moreover, the activated insulin receptor phosphorylates p55PIK in Sf9 cells, and insulin stimulates p55PIK phosphorylation in CHOIR/p55PIK cells. The unique features of p55PIK suggest that it is important in receptor signaling. 相似文献
57.
Tohru Takata Sun Nyunt Wai Akemi Takade Yoshiro Sawae Junko Ono Kazunobu Amako 《Microbiology and immunology》1995,39(9):639-645
From plate cultures of Campylobacter jejuni grown in room air a particulate protein of 62 kDa was isolated by ion-exchange chromatography. The protein had a square shape from the side view but when viewed from the top it had a star-shaped structure. The molecular size of the whole particle determined by gel filtration was 850 kDa which suggested the presence of 14 subunits of 62 kDa in each particle. The N-terminal 37 amino residues showed more than 80% homology with the sequence of these heat shock protein (HSP) 60 homologs of Chlamydia trachomatis, Helicobacter pylori, and Escherichia coli (GroEL). This protein is immunologically cross-reactive with the antiserum for the 60-kDa HSP of Yersinia enterocolitica. Production of the 62-kDa protein increased under heat stress and growth in an aerobic atmospheric environment. From these observations we concluded that the 62-kDa protein is a Campylobacter stress protein (Cj62) which belongs to the HSP 60 family. 相似文献
58.
在96孔板中进行抗脂质过氧化的微量测定 总被引:8,自引:0,他引:8
以Fe2+/半胱氨酸诱导大鼠肝微粒体为基本模型,根据硫代巴比妥酸(TBA)反应原理,优化不同反应条件,建立了一种在96孔板上进行抗脂质过氧化测定的一步反应方法,该方法的灵敏度不低于传统的试管法,而且还具有微量、快速、简便等优点,特别适用于大规模筛选和研究抗氧化剂.此外,也可用于其它系统诱导的抗脂质过氧化的测定. 相似文献
59.
A study of the oxidation of prostacyclin and some of its analogs by three 15-hydroxyprostaglandin dehydrogenases was undertaken to determine the structural features of these compounds which might influence their rate of enzymatic inactivation. The effect of some structural changes seemed to be determined by the substrate specificity of individual enzymes. Other changes influenced the rate of oxidation by all three enzymes similarily. Among this latter group it was noted that a 15S hydroxyl group is necessary for oxidation to occur and that steric changes in the carboxy side chain and structural changes in the epoxy ring have a greater effect on the affinity of the substrate for the enzyme than on its maximum rate of oxidation. Certain analogs of prostacyclin are not substrates for one or more of the enzymes tested. Of these, (5S)-9-deoxy-5,9 alpha-epoxy-PGF1 and its methyl ester are potent inhibitors of only the placental enzyme---an interesting case of apparent selective metabolic regulation. 相似文献
60.
Transplasma membrane electron transport, as assayed by external ferricyanide reduction, has been related to control of growth and hormone response of cells. Elicitor-stimulated transmembrane NADPH oxidase is important for bacteriocidal superoxide production by neutrophils. Since adriamycin is myelosuppressive and can stimulate superoxide production, its effects on the two redox systems of porcine neutrophil plasma membranes were compared. Adriamycin inhibits transplasma membrane ferricyanide and stimulates superoxide production activated by phorbol myristate acetate (PMA). Ferricyanide reduction in PMA-treated cells becomes resistant to inhibition by adriamycin. These results provide evidence for an independent effect of adriamycin on transmembrane ferricyanide reduction and on superoxide generation. 相似文献