Synthesis and structural characterization of two cis-dioxorhenium(V) ReO2[SN][P] mixed-ligand complexes

Two novel five-coordinate cis-dioxorhenium(V) complexes of the general formula ReO₂[R₂NCH₂CH₂S][PPh₃] (R₂N=Et₂N, complex 1 and R₂N=(o-CH₃O---C₆H₄N(CH₂CH₂)₂N, complex 2) have been synthesized by reacting ReOCl₃(PPh₃)₂ with the respective bidentate ligands R₂NCH₂CH₂SH. The complexes have been characterized by elemental analysis, IR, NMR spectroscopies and X-ray crystallography. X-ray crystallographic studies showed that the coordination geometry around rhenium is distorted trigonal bipyramidal. The basal plane is defined by the two doubly bonded oxygen atoms and the sulfur of the bidentate ligand, while the nitrogen of the ligand and the phosphorus occupy the apical positions.     

定向进化人α型干扰素基因家族的研究

应用DNA改组(DNAshuffling)技术重组了12种人α型干扰素基因,并结合噬菌体表面呈现(phagedisplay)技术构建了噬菌体干扰素改组文库,采用简便的、功能性的定向竞争筛选方法,获得了比活达1 0×109IU/mg的新型α型基因工程复合干扰素,是目前国际上已投产的α2型干扰素的5倍,具有生产应用前景,上述策略也为其它细胞因子或酶的改造提供了借鉴方法。     

Haplotypic variation of the transporter associated with antigen processing (TAP) genes and their extension of HLA class II region haplotypes

Stable cell surface presentation of HLA class I molecules requires active transport of antigenic peptides across the endoplasmic reticulum by products of two genes, TAP1 and TAP2, which map in the major histocompatibility complex class II region. Alleles of each gene are derived from a combination of variable sitesaat each locus. In this study, TAP1 and TAP2 alleles were identified in homozygous typing cell (HTC) lines, allowing resolution of specific haplotypes in conjunction with the highly polymorphic HLA class II region haplotypes. Three alleles at each TAP locus were found from which eight haplotypes could be assigned. Determination of TAP1 and TAP2 alleles in cell lines homozygous at DR, DQ, and DP created eight additional haplotypes beyond the number observed with these class II genes alone. Complete analysis of DR, DQ, TAP, and DP genotypes in 66 HTCs resulted in the following groups: 1) 46 homozygotes; 2) nine homozygous at DR, DQ, and TAP, but heterozygous at DP; 3) four homozygous at DR, DQ, and DP, but heterozygous at one or both TAP genes; 4) four homozygous at DR and DQ, but heterozygous at TAP and DP; and 5) three complex genotypes heterozygous at DP, TAP, and at least one of DQA1, DQB1, or DRB1 loci. TAP1 and TAP2 genes map in an area of frequent recombination. TAP alleles were determined in five DQB1, DPB1 recombinant individuals, three of which were informative. Recombination was found between DQB1 and the TAP loci in two individuals and between TAP and DPB1 in the other individual.     

Tissue kinetics,ion transport,and recruitment of mitochondria-rich cells in the skin of the toad (Bufo bufo) in response to exposure to distilled water

Mitochondria-rich cells (MRC) of the amphibian epidermis are responsible for active chloride uptake at low external salinity, and new MRCs are recruited in response to exposure to distilled (deionized) water. The time-course of this recruitment, the tissue kinetics and ion transport have been studied in toads (Bufo bufo) immediately before, and after 2,7, and 14 days exposure to distilled water. General epidermal structure was not affected. However, the numbers of MRCs per mm² (D_MRC) increased throughout the experiment as revealed by staining of epidermal sheets with AgNO₃ (Ag) or methylene blue (MB). Part of the increased D_MRC was accounted for by an increase in MRC subpopulation(s) that stained neither with Ag nor MB. The cell birth rate (K_b) decreased and cell loss by moulting (K_d) increased without any significant change in epidermal cell pool size, indicating a reduced apoptotic rate. The increase in D_MRC was accompanied by a 3-fold increase in Cl^- current (I_Cl). At day-2 there was a transient reduction in the I_Cl per MRC. H⁺ secretion was progressively reduced during prolonged exposure to distilled water. Thus, at day-2 MRCs appeared incompletely differentiated as indicated by decreased I_Cl and H⁺ flux per MRC, and by the increased proportion of MRCs unstained by Ag or MB. Full Cl^- (but not H⁺) transport capacity, was restored at day-7. We conclude that increased D_MRC following exposure to low external Cl^-, rather than being due to an increased K_b, is the combined effect of a decreased apoptotic rate and an increased rate of differentiation, where morphological differentiation precedes functional differentiation.Parts of this study have been presented at the 32th International Congress of Physiological Sciences, 1–6 August, 1993, Glasgow, Scotland, and the 19th meeting of the European Study Group for Cell Proliferation, 5–9 October, 1993, Bruges, Belgium     

Translocation by the RecB motor is an absolute requirement for {chi}-recognition and RecA protein loading by RecBCD enzyme

RecBCD enzyme is a heterotrimeric helicase/nuclease that initiates homologous recombination at double-stranded DNA breaks. The enzyme is driven by two motor subunits, RecB and RecD, translocating on opposite single-strands of the DNA duplex. Here we provide evidence that, although both motor subunits can support the translocation activity for the enzyme, the activity of the RecB subunit is necessary for proper function of the enzyme both in vivo and in vitro. We demonstrate that the RecBCD(K177Q) enzyme, in which RecD helicase is disabled by mutation of the ATPase active site, complements recBCD deletion in vivo and displays all of the enzymatic activities that are characteristic of the wild-type enzyme in vitro. These include helicase and nuclease activities and the abilities to recognize the recombination hotspot chi and to coordinate the loading of RecA protein onto the ssDNA it produces. In contrast, the RecB(K29Q)CD enzyme, carrying a mutation in the ATPase site of RecB helicase, fails to complement recBCD deletion in vivo. We further show that even though RecB(K29Q)CD enzyme displays helicase and nuclease activities, its inability to translocate along the 3'-terminated strand results in the failure to recognize chi and to load RecA protein. Our findings argue that translocation by the RecB motor is required to deliver RecC subunit to chi, whereas the RecD subunit has a dispensable motor activity but an indispensable regulatory function.     

Allelic repertoire of the humanMHC class IMICA gene

 The hallmark of the classical major histocompatibility complex (MHC) class I molecules is their astonishing level of polymorphism, a characteristic not shared by the nonclassical MHC class I genes. A distinct family of MHC class I genes has been recently identified within the human MHC class I region. The MICA (MHC class I chain-related A) gene in this family is a highly divergent member of the MHC class I family and has a unique pattern of tissue expression. We have sequenced exons encoding the extracellular α1, α2, and α3 domains of the MICA gene from twenty HLA homozygous typing cell lines and four unrelated individuals. We report the identification of eleven new alleles defined by a total of twenty-two amino acid substitutions. Thus, the total number of MICA alleles is sixteen. Interestingly, a tentative superimposition of MICA variable residues on the HLA-A2 structure reveals a unique pattern of distribution, concentrated primarily on the outer edge of the MICA putative antigen binding cleft, apparently bordering an invariant ligand binding site. Received: 13 May 1996 / Revised: 29 May 1996     

The biosynthesis of ovothiol A (N-methyl-4-mercaptohistidine). Identification of S-(4'-L-histidyl)-L-cysteine sulfoxide as an intermediate and the products of the sulfoxide lyase reaction.

Crude extracts of Crithidia fasciculata catalyse the formation of 4-mercapto-L-histidine, an intermediate in the biosynthesis of ovothiol A (N1-methyl-4-mercaptohistidine), in the presence of histidine, cysteine, Fe2+ and pyridoxal phosphate. This activity was present in a 35-55% ammonium sulfate fraction that was shown to produce a transsulfuration intermediate in the absence of pyridoxal phosphate. The transsulfuration intermediate was isolated and identified as S-(4'-L-histidyl)-L-cysteine sulfoxide. The synthase activity, partially purified by anion-exchange chromatography, was shown to require oxygen and could be used to synthesize a number of isotopically labeled S-(4'-L-histidyl)-L-cysteine sulfoxides. Sulfoxide lyase activity was partially resolved from the synthase by anion-exchange chromatography. The phenylhydrazone of the product derived from the cysteine moiety of the sulfoxide coeluted with the phenylhydrazone of pyruvate on HPLC, but this assignment could not be confirmed by mass spectral analysis. S-(4'-[14C]L-histidyl)-[U-13C3,15N]L-cysteine sulfoxide was synthesized and converted to products of the lyase reaction in the presence of lactate dehydrogenase and NADH. The 13C-labeled product was identified by 13C-NMR spectroscopy as lactate and the primary product of the lyase reaction is therefore pyruvate. With S-(4'[3H]L-histidyl)-[14C]L-cysteine sulfoxide as the substrate [14C]lactate, [14C]cysteine and [3H]4-mercaptohistidine could be detected as products of the lyase reaction, but the sum of the two thiol species exceeded the amount of sulfoxide substrate used. Evidence is presented that this anomaly was due to the utilization of sulfur from dithiothreitol for the formation of cysteine.     

Mixed-ligand technetium(III) complexes with tetradendate/monodendate NS(3)/isocyanide coordination: a new nonpolar technetium chelate system for the design of neutral and lipophilic complexes stable in vivo.

Starting from the tripodal ligand 2,2',2' '-nitrilotris(ethanethiol) (NS(3)) and isocyanides (CNR) as co-ligands, neutral mixed-ligand technetium(III) complexes of the general formulation [Tc(NS(3))(CNR)] have been synthesized and characterized. The (99)Tc complexes can be( )()obtained by a two-step reduction/substitution procedure starting from [TcO(4)](-) via the phosphine-containing precursor complex [Tc(NS(3))(PMe(2)Ph)]. As shown by X-ray structural analyses, the complexes adopt a nearly ideal trigonal-bipyramidal geometry with the trigonal plane formed by the three thiolate sulfurs of the tripodal ligand. The central nitrogen atom of the chelate ligand and the monodendate isocyanides occupy the apical positions. The no-carrier-added preparation of the corresponding (99m)Tc complexes was performed by a one-step procedure starting from (99m)[TcO(4)](-) with stannous chloride as reducing agent. Biodistribution studies in the rat demonstrated for the nonpolar, lipophilic compounds a significant initial brain uptake. In vitro challenge experiments with glutathione clearly indicated that no transchelation reaction occurs. Furthermore, there were no indications for reoxidation of Tc(III) to Tc(V) species or pertechnetate. We propose this type of complexes as a useful tool in the design of lipophilic (99m)Tc or (186)Re/(188)Re radiopharmaceuticals.