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51.
P K Paul P Dauber-Osguthorpe M M Campbell D J Osguthorpe 《Biochemical and biophysical research communications》1989,165(3):1051-1058
A 50 pico-second molecular dynamics simulation on a cyclic LHRH antagonist analogue Ac-D-Phe1-D-Phe2-D-Trp3-Ser4-Glu5-D-Arg6-Leu7-Lys8+ ++-Pro9-D-Ala10-NH2 (where the cyclisation is via an amide linkage between the Glu5 and Lys8 side chains), reveals some hitherto unseen conformational features. The LHRH analogue is found to adopt a near beta-sheet type of conformation with the reversal in the chain being brought about by a D-Trp3-Ser4-Glu5-D-Arg6 beta turn. The N- and C-terminal ends of the peptide come close together and interact through a network of hydrogen bonds. Additional hydrogen bonds expected of a sheet type of conformation stabilise the lowest energy minima. A conformational search of all possible cyclic structures of a model system c(Glu-D-Ala-Ala-Lys) which was used to determine the starting structure for the simulation studies of the cyclic LHRH antagonist analogue is also highlighted. The influence of the cyclic part on the conformation of this LHRH analogue is discussed. 相似文献
52.
An unstable carboxypeptidase N or B like enzyme is generated as a result of coagulation. This enzyme is derived from some plasma component (s) and not from blood cells or platelets. Furthermore, the activity generated is specific for arginine substrates insofar as small synthetic substrates are concerned. The enzyme is unrelated to CPN or any of its subunits or subunit fragments. This transient carboxypeptidase may be involved in the processing and/or scheduling of different functions of bioactive peptides generated during inflammation. 相似文献
53.
Use of a rapid bioluminescence assay for detecting cyanobacterial microcystin toxicity 总被引:2,自引:0,他引:2
L. A. Lawton D. L. Campbell K. A. Beattie G. A. Codd 《Letters in applied microbiology》1990,11(4):205-207
The recent rise in the awareness of the occurrence of toxic cyanobacterial blooms in aquatic environments, with associated human health problems and animal deaths, has increased the need for rapid, reliable and sensitive methods of determining cyanobacterial toxicity. A luminescent bacterial toxicity test was assessed as a complement to the established mouse bioassay. Seventeen samples including pure cyanobacterial microcystin-LR hepatotoxin, laboratory isolates and natural blooms of cyanobacteria were tested and toxicity data compared with mouse LD50 values. Microcystin-LR and all five microcystin-containing cyanobacterial samples, hepatotoxic by mouse test gave EC50 values of less than 0.46 mg/ml in bioluminescence-based Microtox assays. Of 11 samples non-toxic by mouse bioassay, only two gave an EC50 of less than 0.98 mg/ml by bioluminescence assay. It is suggested that the Microtox bioluminescence assay may prove useful in the preliminary screening of cyanobacterial blooms for microcystin-based toxicity. 相似文献
54.
55.
Identification of trans-dominant HIV-1 rev protein mutants by direct transfer of bacterially produced proteins into human cells. 总被引:36,自引:1,他引:35 下载免费PDF全文
A synthetic rev gene containing substitutions which introduced unique restriction sites but did not alter the deduced amino acid sequence was used as a vehicle to construct mutations in rev. Insertion or substitution mutations within a domain of Rev resulted in proteins able to inhibit the function of Rev protein in trans. Rev function was monitored in a cell line, HLfB, which contained a rev- mutant provirus. HLfB cells require the presence of rev for virus production, which was conveniently monitored by immunoblot detection of p24gag. Trans-dominant mutants were identified after expression in bacteria and delivery into HLfB cells by protoplast fusion. In addition, the trans-dominant phenotype was verified by expression of the mutant proteins in HLfB cells after cotransfection. These studies define a region between amino acid residues 81 and 88 of rev, in which different mutations result in proteins capable of inhibiting Rev function. 相似文献
56.
Purification of the NADPH:5 alpha-dihydroprogesterone 3 alpha-hydroxysteroid oxidoreductase from female rat pituitary cytosol 总被引:1,自引:0,他引:1
J S Campbell H J Karavolas 《The Journal of steroid biochemistry and molecular biology》1990,37(2):215-222
The NADPH:5 alpha-dihydroprogesterone 3 alpha-hydroxysteroid oxidoreductase (3 alpha-HSOR) [EC 1.1.1.50] which catalyzes the reversible conversion of 5 alpha-pregnane-3,20-dione (5 alpha-dihydroprogesterone; 5 alpha-DHP) to 3 alpha-hydroxy-5 alpha-pregnan- 20-one (3 alpha-,5 alpha-tetrahydroprogesterone; 3 alpha,5 alpha-THP) was purified to apparent homogeneity from female rat anterior pituitary cytosol by a three step micro-purification procedure. Specific activity of purified 3 alpha-HSOR was enriched 438-fold from that in pituitary cytosol using successive ion exchange, chromatofocusing and affinity column chromatography purification steps. 3 alpha-HSOR appears to be a monomer with an approximate molecular weight of 36 kDa and an isoelectric point of about 5.75. The purified enzyme appears as a single protein staining band (36 kDa) when examined by polyacrylamide gel electrophoresis and with both silver or Coomassie blue staining. Under non-dissociating electrophoretic conditions, all of the 3 alpha-HSOR activity co-migrated with the 36 kDa protein staining band. The purified enzyme in the presence of the preferred cofactor, NADPH, has an apparent Km for 5 alpha-DHP of 82 nM and a Vmax of 1.2 mumol of 3 alpha,5 alpha-THP formed per mg protein/30 min. The Km for NADPH was 0.71 microM. In the oxidative direction, the enzyme in the presence of NADP+ has a Km for 3 alpha,5 alpha-THP of 1.4 microM and a Vmax of 9.7 mumol of 5 alpha-DHP formed per mg protein/30 min. The Km for NADP+ was 1.6 microM. 相似文献
57.
58.
Catabolic instability,plasmid gene deletion and recombination in Alcaligenes sp. BR60 总被引:12,自引:0,他引:12
An Alcaligenes sp. BR60, isolated from surface runoff waters of the Hyde Park industrial landfill, contained a novel 85 kb catabolic plasmid (pBR60) functional in 3-chlorobenzoate (3Cba) degradation. The plasmid exhibited a spontaneous 3.2% frequency of deletion of a 14 kb fragment specifying 3Cba degradation. The deletion mutant BR40 and mitomycin C cured strains were not able to grow on 3Cba and had reversion frequencies of less than 10-10 cell-1 generation-1. Transformation or conjugation of pBR60 into cured strains restored catabolic activity. An EcoRI, BgIII, HindIII and SaII restriction map of the deletion region was constructed, and EcoRI and HindIII fragments spanning the deletion region of the plasmid were cloned in pUC18. Conjugation of resistance plasmid R 68.45 into Alcaligenes sp. BR60, with selection on antibiotics, resulted in the elimination of pBR60 and maintenance of unaltered R68.45. In 30% of the exconjugants, 3Cba degradative capacity was retained, although variation in the regulation of 3Cba degradation was observed in these strains. Hybridization of deletion region fragments to BgIII digested total DNA of BR60 and the R68.45 cured exconjugants revealed the presence of pBR60 deletion region sequences in the chromosome of exconjugants. Hybridization also revealed a repeated sequence flanking the deletion region of pBR60. Selection on 4-chlorobenzoate as a sole source of carbon and energy resulted in the isolation of 4Cba+ mutants of Alcaligenes sp. BR60.Abbreviations 3 and 4 Cba
chlorobenzoic acid isomers and growth phenotypes
- HPLC
high pressure liquid chromatography
- ATCC
American Type Culture Collection 相似文献
59.
John G. Carman Nancy E. Jefferson William F. Campbell 《Plant Cell, Tissue and Organ Culture》1988,12(1):83-95
Somatic embryo (embryoid) formation from immature-embryo-derived calli was quantified in replicated experiments involving 10Triticum aestivum L. genotypes. Several published media formulations, which had previously been optimized for wheat tissue culture, were tested for each genotype. Embryos from each plant were randomly assigned to each medium. Percentage precocious germination of immature embryos and mean percentage scutellar callus per explant were recorded. Embryoids per callus were determined by microscopic examination at 28 and 56 days. There were highly significant differences among genotypes, media, and individual plants from which explants were taken. A medium based on double the Murashige and Skoog (MS) inorganic salt concentration was significantly better than other media. Inclusion of all MS vitamins appeared essential for optimal response. Two genotypes were tested in a second experiment where both 3,6-dichloro-o-anisic acid (9.05 M) and 6-furfurylaminopurine (0.46 M) were substituted for 2,4-dichlorophenoxyacetic acid (4.52 M) in either double or normal MS medium. This substitution significantly increased embryoid formation at 28 days. Additions of either 6-furfurylaminopurine or coconut water increased precocious germination of both embryo explants and embryoids.This study was supported in part by NASA-Ames Cooperative Agreement No. NCC2-139. Contribution of the Utah Agricultural Experiment Station, Utah State University, Logan, UT, Journal Paper No. 3358. 相似文献
60.
Nitrate reductase and its role in nitrate assimilation in plants 总被引:16,自引:0,他引:16
Wilbur H. Campbell 《Physiologia plantarum》1988,74(1):214-219
Nitrate reductase (EC 1.6.6.1) is an enzyme found in most higher plants and appears to be a key regulator of nitrate assimilation as a result of enzyme induction by nitrate. The biochemistry of nitrate reductase has been elucidated to a great extent and the role that nitrate reductase plays in regulation of nitrate assimilation is becoming understood. 相似文献