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121.
Prevotella ruminicola plays a prominent role in the breakdown of peptides in the rumen, a process which contributes to excessive ammonia production and inefficient nitrogen retention in ruminants. Various metal ions and chelators were examined to assess how the metal ion-dependent dipeptidase activity of P. ruminicola M384 might be inhibited. Using sonicated extracts, Cu2+ , Cr2+ and Hg2+ were most inhibitory, decreasing Ala2 breakdown to 15, 15 and 5% of control activity, whereas Co2+ , Mn2+ and Zn2+ stimulated activity by 189, 30 and 26%, respectively. The chelators, EDTA, EGTA, TPEN and 1,10-phenanthroline, were inhibitory, as were several phenanthroline analogues. Among the stereoisomers of 1,10-phenanthroline tested, derivatives methylated on C-2 and C-9 were less effective than the parent molecule, but 3,4,7,8-tetramethyl,10-phenanthroline (TMP) was more inhibitory. Titration of the most effective inhibitors showed that EDTA, TPEN and TMP had similar potency and were effective at 0.1 mmol l−1 and above. Thus some metal ions and chelators are potent inhibitors of P. ruminicola dipeptidase, although they are unlikely to be sufficiently specific to peptide metabolism to be useful in vivo. 相似文献
122.
The use of selective and differential agars in the isolation of Escherichia coli O157 from dairy herds 总被引:1,自引:1,他引:0
The use of selective and differential agars for the isolation of Escherichia coli O157 from the faeces of dairy herds was investigated. Out of the 614 isolates which were positive for one or more of the selective criteria employed in the media only four proved to be E. coli O157. Ninety-nine per cent of the isolates were false positives. The procedure which resulted in the isolation of E. coli O157 from faecal samples was enrichment in modified Tryptone Soya Broth supplemented with novobiocin and subsequent growth on Chromagar O157. 相似文献
123.
Koichi Matsuzaki Mikio Kan Wallace L. McKeehan 《In vitro cellular & developmental biology. Animal》1996,32(6):345-360
Summary Two transmembrane serine-threonine kinases (type I and II receptors), a membrane-anchored proteoglycan (type III), and a homodimeric
ligand participate in the transforming growth factor beta type on (TGFβ1) signal transduction complex. The expression of recombinant
receptors in insect cells co-infected with up to three recombinant baculoviruses was employed to study interactions among
the ectodomains of the three types of receptors and the TGFβ1 ligand in absence of uncontrollable extrinsic factors in mammalian
cells. Multi-subunit complexes were assembled in intact cells and purified on glutathione-conjugated beads for analysis by
tagging one of the subunits with glutathione S-transferase (GST). Intrinsic ligand-independent interactions were observed
among receptor subunits as follows: type III–III type I–I, type III-I, and type II-I. The homeotypic complex of type II–II
receptors and the heterotypic type III-II interaction was ligand dependent. The type I, but not the type III, subunit displaced
about 50% of the type II component in either ligand-dependent homomeric type II-type II complexes or heteromeric type III-type
II complexes to form type II-I or type III-II-I oligomers, respectively. The type II subunit displaced type I subunits in
oligomers of the type I subunit. Specificity of type I receptors may result from differential affinity for the type II receptor
rather than specificity for ligand. A monomeric subunit of the TGFβ1 ligand bound concurrently to type III and type II or
type III and type I receptors, but failed to concurrently bind to the type II and type I subunits. The binding of TGFβ1 to
the type I kinase subunit appears to require an intact disulfide-linked ligand dimer in the absence of a type III subunit.
The combined results suggest a pentameric TGFβ signal transduction complex in which one unit each of the type III, type II,
and type I components is assembled around the two subunits of the dimeric TGFβ1 ligand. An immobilized GST-tagged subunit
of the receptor complex was utilized to assemble multi-subunit complexesin vitro and to study the phosphorylation events among subunits in the absence of extrinsic cell-derived kinases. The results revealed
that (a) a low level of ligand-independent autophosphorylation occurs in the type I kinase; (b) a high level of autophosphorylation
occurs in the type II kinase; (c) both the type III and type I subunits aretrans-phosphorylated by the type II subunit; and (d) the presence of both type I and II kinases complexed with the type III subunit
and dimeric TGFβ1 ligand in a pentameric complex causes maximum phosphorylation of all three receptor subunits. 相似文献
124.
Yong Xu Wallace G. Buchholz Richard T. DeRose Timothy C. Hall 《Plant molecular biology》1995,27(2):237-248
Two cDNA clones (RCc2 and RCc3) corresponding to mRNAs highly expressed only in root tissues of rice (Oryza sativa L.) seedlings were characterized. Respectively, they encode polypeptides of 146 (14.5 kDa) and 133 amino acids (13.4 kDa) that share high (<70%) sequence similarity with a polypeptide encoded by a cDNA (ZRP3) encoding an mRNA preferentially expressed in young maize roots. Genomic DNA blot analysis revealed that they are members of a small gene family and RCg2, the gene corresponding to RCc2, was isolated. A 1656 bp 5-upstream sequence of RCg2 was translationally fused to a -glucuronidase (GUS) reporter gene and stable introduction of the chimeric construct into rice was confirmed by PCR and genomic DNA blot analyses. Histochemical analysis of transgenic rice plants containing the full-length chimeric gene showed high levels of GUS activity in mature cells and the elongation and maturation zones of primary and secondary roots, and in the root caps, but no GUS activity was detected in root meristematic regions. Surprisingly, high GUS activity was also detected in leaves of the same plants. This raises the possibility that the RCg2 5-upstream element may not be sufficient for the proper spatial control of root specificity in transgenic rice. 相似文献
125.
L. C. Folmar N. D. Denslow † R. A. Wallace ‡ G. LaFleur ‡ T. S. Gross § S. Bonomelli § C. V. Sullivan | 《Journal of fish biology》1995,46(2):255-263
126.
Over the past decade, much has been learned regarding the role of various cytokines in the pathogenesis of inflammatory bowel disease. Several cytokine 'knockout' models in mice have been shown to develop colitis, while alterations in the production of various cytokines has been documented in human Crohn's disease and ulcerative colitis. In recent years, attempts have been made to treat these diseases through modulation of cytokine production or action. This review focuses on the cytokines that have been implicated in the pathogenesis of inflammatory bowel disease. The evidence for and against a role for particular cytokines in intestinal inflammation is reviewed, as is the experimental and clinical data suggesting that cytokines are rational targets for the development of new therapies. 相似文献
127.
Transient Ischemia Differentially Increases Tyrosine Phosphorylation of NMDA Receptor Subunits 2A and 2B 总被引:9,自引:4,他引:5
Norio Takagi Kiyohito Shinno Lucy Teves Nankie Bissoon M. Christopher Wallace James W. Gurd 《Journal of neurochemistry》1997,69(3):1060-1065
Abstract: Activation of the N -methyl- d -aspartate (NMDA) receptor has been implicated in the events leading to ischemia-induced neuronal cell death. Recent studies have indicated that the properties of the NMDA receptor channel may be regulated by tyrosine phosphorylation. We have therefore examined the effects of transient cerebral ischemia on the tyrosine phosphorylation of NMDA receptor subunits NR2A and NR2B in different regions of the rat brain. Transient (15 min) global ischemia was produced by the four-vessel occlusion procedure. The tyrosine phosphorylation of NR2A and NR2B subunits was examined by immunoprecipitation with anti-tyrosine phosphate antibodies followed by immunoblotting with antibodies specific for NR2A or NR2B, and by immunoprecipitation with subunit-specific antibodies followed by immunoblotting with anti-phosphotyrosine antibodies. Transient ischemia followed by reperfusion induced large (23–29-fold relative to sham-operated controls), rapid (within 15 min of reperfusion), and sustained (for at least 24 h) increases in the tyrosine phosphorylation of NR2A and smaller increases in that of NR2B in the hippocampus. Ischemia-induced tyrosine phosphorylation of NR2 subunits in the hippocampus was higher than that of cortical and striatal NR2 subunits. The enhanced tyrosine phosphorylation of NR2A or NR2B may contribute to alterations in NMDA receptor function or in signaling pathways in the postischemic brain and may be related to pathogenic events leading to neuronal death. 相似文献
128.
Analysis of mtDNA variation in African populations reveals the most ancient of all human continent-specific haplogroups. 总被引:25,自引:13,他引:12
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Y S Chen A Torroni L Excoffier A S Santachiara-Benerecetti D C Wallace 《American journal of human genetics》1995,57(1):133-149
mtDNA sequence variation was examined in 140 Africans, including Pygmies from Zaire and Central African Republic (C.A.R.) and Mandenkalu, Wolof, and Pular from Senegal. More than 76% of the African mtDNAs (100% of the Pygmies and 67.3% of the Senegalese) formed one major mtDNA cluster (haplogroup L) defined by an African-specific HpaI site gain at nucleotide pair (np) 3592. Additional mutations subdivided haplogroup L into two subhaplogroups, each encompassing both Pygmy and Senegalese mtDNAs. A novel 12-bp homoplasmic insertion in the intergenic region between tRNA(Tyr) and cytochrome oxidase I (COI) genes was also observed in 17.6% of the Pygmies from C.A.R. This insertion is one of the largest observed in human mtDNAs. Another 25% of the Pygmy mtDNAs harbored a 9-bp deletion between the cytochrome oxidase II (COII) and tRNA(Lys) genes, a length polymorphism previously reported in non-African populations. In addition to haplogroup L, other haplogroups were observed in the Senegalese. These haplogroups were more similar to those observed in Europeans and Asians than to haplogroup L mtDNAs, suggesting that the African mtDNAs without the HpaI np 3592 site could be the ancestral types from which European and Asian mtDNAs were derived. Comparison of the intrapopulation sequence divergence in African and non-African populations confirms that African populations exhibit the largest extent of mtDNA variation, a result that further supports the hypothesis that Africans represent the most ancient human group and that all modern humans have a common and recent African origin. The age of the total African variation was estimated to be 101,000-133,000 years before present (YBP), while the age of haplogroup L was estimated at 98,000-130,000 YBP. These values substantially exceed the ages of all Asian- and European-specific mtDNA haplogroups. 相似文献
129.
Identification of a yeast artificial chromosome clone spanning a translocation breakpoint at 7q32.1 in a Smith-Lemli-Opitz syndrome patient. 总被引:2,自引:0,他引:2
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T L Alley B A Gray S H Lee S W Scherer L C Tsui G S Tint C A Williams R Zori M R Wallace 《American journal of human genetics》1995,56(6):1411-1416
Smith-Lemli-Opitz syndrome (SLOS) is a mental retardation/multiple congenital anomaly syndrome. The gene(s) involved has not been mapped or cloned, but, recently, a biochemical abnormality in cholesterol biosynthesis has been shown to occur in most SLOS patients. The defect is suspected to occur in the penultimate step of the cholesterol pathway, involving the enzyme 7-dehydrocholesterol reductase, which has not been isolated. On the basis of the hypothesis that a de novo balanced translocation [t(7;20)(q32.1;q13.2)] in an SLOS patient directly interrupts the SLOS gene, positional cloning techniques are being employed to localize and identify the SLOS gene. We report the identification of a chromosome 7-specific YAC that spans the translocation breakpoint, as detected by FISH. This is the first study narrowing a candidate SLOS region and placing it on physical and genetic maps of the human genome. 相似文献
130.
Roberta S. Wallace J. Andrew Teare Edward Diebold Margaret Michaels Mary Jo Willis 《Zoo biology》1995,14(4):311-316
To establish baseline hematologic and plasma biochemistry values in free-ranging Humboldt penguins (Spheniscus humboldti), heparinized blood samples were collected from 51 apparently healthy, adult Humboldt penguins residing at two colonies off the Chilean coast. Thirty samples were collected in April, 1992, from penguins inhabiting the Ex-islote de los Pájaros Niños in Algarrobo, Chile. In September, 1992, 21 samples were collected from birds inhabiting Isla de Cachagua, Chile. Hematologic values measured include packed cell volume, leucocyte count, leucocyte differential, and the presence of blood parasites. Plasma biochemistry values measured include glucose, blood urea nitrogen, creatinine, uric acid, calcium, inorganic phosphorous, sodium, potassium, chloride, total protein, albumin, globulin, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, total bilirubin, and creatine kinase. Only the mean values for chloride and for the number of eosinophils differed significantly between the two sample groups. No blood parasites were seen. © 1995 Wiley-Liss, Inc. 相似文献