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101.
C5 convertase of the alternative complement pathway: covalent linkage between two C3b molecules within the trimolecular complex enzyme 总被引:3,自引:0,他引:3
T Kinoshita Y Takata H Kozono J Takeda K S Hong K Inoue 《Journal of immunology (Baltimore, Md. : 1950)》1988,141(11):3895-3901
C5 convertase of the alternative C pathway is a complex enzyme consisting of three C fragments--one molecule of a major fragment of factor B (Bb) and two molecules of a major fragment of C3 (C3b). Within this C3bBbC3b complex, the first C3b binds covalently to the target surface, and Bb, which bears a catalytic site, binds noncovalently to the first C3b. In the present investigation, we studied the nature of the convertase that is assembled on E surfaces and obtained evidence that the second C3b binds directly to the alpha'-chain of the first through an ester bond rather than to the target surface. Thus, the alternative pathway C5 convertase could be described as a trimolecular complex in which Bb binds noncovalently to a covalently linked C3b dimer. We also obtained evidence that not only the second C3b but also the first C3b participates in binding C5, that is, covalently-linked C3b dimer acts as a substrate-binding site. Because of this two-site binding, the convertase has a much higher affinity for C5 than the surrounding monomeric C3b molecules. Based on this evidence, a new model of the alternative pathway C5 convertase is proposed. Covalent association of two subunits and the bivalent binding of the substrate are then common properties of the alternative and classical pathway C5 convertases. 相似文献
102.
Monoclonal antibodies to mouse complement receptor type 1 (CR1). Their use in a distribution study showing that mouse erythrocytes and platelets are CR1-negative 总被引:14,自引:0,他引:14
T Kinoshita J Takeda K Hong H Kozono H Sakai K Inoue 《Journal of immunology (Baltimore, Md. : 1950)》1988,140(9):3066-3072
mAb to murine C receptor type 1 (CR1) were produced and three of them were characterized. One antibody, designated as 8C12, immunoprecipitated a protein of 190,000 Mr from a detergent extract of surface-labeled spleen cells and stained spleen B but not T lymphocytes in fluorescent flow cytometry. It inhibited both CR1-mediated rosette formation and the cofactor activity of CR1 for factor I-mediated cleavage of C3b, suggesting that it recognizes the ligand-binding site of CR1. The two other antibodies, designated as 7G6 and 7E9, recognized different epitopes from that recognized by 8C12, and they cross-reacted with a protein of 150,000 Mr that is present in a spleen extract. The distribution of CR1 in murine hemopoietic cells was studied by binding experiments with radiolabeled 8C12 and fluorescent flow cytometry. When CR1 was not detected by 8C12 alone, the two other antibodies were used in combination with 8C12 to confirm the negative results. Almost all B lymphocytes from the spleen, lymph nodes, and peripheral blood were CR1 positive. Most of the Thy-1-positive lymphocytes from these tissues were CR1 negative. Thymus lymphocytes were also CR1 negative. Peritoneal macrophages and chemotactic factor stimulated but not unstimulated peripheral blood granulocytes were CR1 positive. In contrast to human E, mouse E were CR1 negative. This pattern of distribution was consistent with previous results obtained by rosette assays. Although mouse platelets cause immune adherence hemagglutination with C3b-bearing SRBC, they are CR1 negative. Three other lines of evidence also indicated that platelets are CR1 negative. First, no band of CR1 was demonstrated by immunoprecipitation with 8C12 of an extract of surface-labeled platelets. Second, 8C12, which inhibited rosette formation by lymphocytes, alone or in combination with 7G6 and 7E9, did not inhibit immune adherence between platelets and C3b-bearing SRBC. Third, polyclonal rabbit IgG prepared from anti-mouse CR1 antiserum did not inhibit immune adherence by platelets. These results strongly suggest that the C3b-binding factor(s) on mouse platelets is different from CR1 and that processing of C3b-bearing immune complexes in mouse blood may be mediated by a new and as yet unidentified C3b-binding factor(s). 相似文献
103.
Genetic organization and nucleotide sequence of the stability locus of IncFII plasmid NR1 总被引:14,自引:0,他引:14
A Tabuchi Y N Min C K Kim Y L Fan D D Womble R H Rownd 《Journal of molecular biology》1988,202(3):511-525
The stability (stb) locus of IncFII plasmid NR1 was mapped to a 1700 base-pair NaeI-TaqI restriction fragment. A series of unstable plasmids that contained insertion, deletion, and point mutations that inactivated the stability function was isolated. The unstable point mutants examined were all stabilized (complemented) in trans by a copy of the wild-type stb locus, suggesting that the mutations had inactivated diffusible gene products. The nucleotide sequence of the stb locus contained two tandem open reading frames, designated stbA and stbB, that encoded essential trans-acting protein products with predicted sizes of 36,000 Mr and 13,000 Mr, respectively. A third open reading frame, stbC, that could encode a peptide of 8000 Mr was contained within stbB in the complementary DNA strand. Plasmid-encoded proteins of 36,000 Mr and 13,000 Mr were identified in minicell experiments as the products of stbA and stbB, respectively. Unstable deletion mutants that retained the promoter proximal region of the stb locus upstream from stbA but had deleted both stbA and stbB were stabilized in trans by plasmids that could supply StbA and StbB. In contrast, deletion mutants that had lost the stbAB promoter region were not complemented in trans, indicating that this region contained an essential cis-acting site (or sites). Unlike some other loci that mediate stable plasmid inheritance, cloned copies of the wild-type stb locus of NR1 did not exert strong incompatibility (i.e. trans destabilization) against other stb+ derivatives of plasmid NR1 present in the same cell. 相似文献
104.
从“湖北光敏感核不育水稻”的未受精子房和花药培养出单倍体植株 总被引:10,自引:0,他引:10
采用10种诱导培养基,培养湖北光敏感核不育水稻农垦58品种的未受精子房和花药。共培养未受精子房2790个,获得胚囊愈伤组织17块,最高诱导频率达3.33%,其中2块分化出绿苗。培养花药16740个,获得花药愈伤组织15块,最高诱导频率为0.92%,其中3块分化出苗,2丛白苗,1株绿苗。胚囊植株和花粉植株经根尖染色体检查为单倍体,2n=x=12。实验证明,液体培养、2,4-D0.2-0.5 mg/1、低温预处理对诱导胚囊愈伤组织及花粉愈伤组织的形成具良好效果。 相似文献
105.
Observation was made on early ontogeny of vascular cambium in the developing root ofGinkgo biloba L. After completion of root elongation, the vascular meristem gradually acquires cambial characteristics. Strips of the periclinal
division of cells in transverse section are observed on the inner side of phloem when the primary xylem and phloem in the
stele have been established. The strips are united into a continuous layer between phloem and xylem. In tangenital section,
the procambium shows a homogeneous structure, which is initially composed of short cells with transverse end walls and subsequently,
of long cells with tapering ends. Then, the procambium is organized into two systems of cells; axial strands of short cells
with transverse end walls resulting from the sporadic transverse divisions of long cells, and long cells with tapering ends.
Still later, the short cells are divided frequently in a trasverse plane exhibiting one or a few cells in width and several
decades of cells in height, while the long cells are elongated. The frequency of transverse divisions of the short cells decreases
in subsequent stages. Eventually, the short cells in axial strands are vertically separated from one another by the elongation
of neighboring long cells and by the decrease in the frequency of transverse divisions of short cells themselves. Cambial
initials occur in two forms; ray initials a few cells in height and one cell in width derived from the short cells, and fusiform
initials with tapering ends derived from the long cells. 相似文献
106.
大鼠应激性胃粘膜损害与eAMPCa~2及能量代谢变化的关系 总被引:1,自引:0,他引:1
本文采用放射免疫测定法、原子吸收光谱分析法和生化酶分析法,测定了大鼠在经受束缚加浸水急性应激四小时内,胃组织cAMP Ca~(2+)及在ATP、ADP、AMP和能量代谢的短期动态变化,同时观察了胃粘膜的损害程度。结果发现胃粘膜损害面积密度随着应激时间延长而逐渐增加;胃组织cAMP和Ca~(2+)则进行性降低;两者呈密切负相关;胃组织能量代谢却略有增强。若预先给以CaCl_2,再予应激,则有减轻应激性胃粘膜损害的作用。 相似文献
108.
TPA对原代白血病细胞的诱导分化作用 总被引:2,自引:0,他引:2
本文报告了TPA对32例不同类型白血病细胞的体外分化诱导结果。TPA(1.6×10~-7M)可诱导急性非淋巴细胞(ANLL)白血病细胞迅速出现单核巨噬细胞分化标志:细胞贴壁、胞浆丝状伪足形成,具有类似巨噬细胞的形态改变及相应的细胞化学反应特征。急性淋巴细胞白血病(ALL)和桨细胞白血病(PCL)细胞不发生上述变化,表现为细胞聚集成闭现象。慢性淋巴细胞白血病(CLL)出现桨细胞样形态转化。初发与复发病例的诱导反应相类似。TPA体外诱导分化实验,有助于了解病人白血病细胞的分化潜能,对于鉴别粒单系和淋巴系两类白血病,尤其对于用常规方法分型困难的低分化白血病有一定的临床诊断意义。 相似文献
109.
110.
<正> 近年来,光敏亲和标记技术已被广泛应用于激素及共受体,蛋白和核酸的相互作用、酶的结构与功能、膜蛋白结构、tRNA同共合成酶的识别等研究上,鉴于ATP是某些酶的底物,因此合成光敏的ATP底物类似物将有助于国内对达些酶的结构与功能进行深入研究,为此我们合成了8-N_8-5′-ATP,现将实验结果报道如下: 相似文献