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151.
The effects of essential amino acids on albumin synthesis by a mouse hepatoma cell line have been investigated. The amino acids tested were tryptophan, phenylalanine, histidine, isoleucine and leucine. Cellular rates of synthesis (molecules albumin/cell per min) were determined from rates of [3H]leucine incorporation into immunoprecipitable albumin in the culture medium. The effects of amino acids on albumin synthesis fall into three distinct groups. The concentration of tryptophan producing half-maximal synthesis is 4 micronM. The corresponding concentration for leucine is 100 micronM. Histidine, phenylalanine and isoleucine were very similar, the half-maximal concentrations being approximately 15 micronM. The concentrations of amino acids producing half-maximal synthesis correlate directly with the amino acid composition of albumin. The levels of these essential amino acids necessary to saturate albumin synthesis have been compared with amino acid levels in normal plasma. 相似文献
152.
Isolation and characterization of griffithsin, a novel HIV-inactivating protein, from the red alga Griffithsia sp 总被引:2,自引:0,他引:2
Mori T O'Keefe BR Sowder RC Bringans S Gardella R Berg S Cochran P Turpin JA Buckheit RW McMahon JB Boyd MR 《The Journal of biological chemistry》2005,280(10):9345-9353
Griffithsin (GRFT), a novel anti-HIV protein, was isolated from an aqueous extract of the red alga Griffithsia sp. The 121-amino acid sequence of GRFT has been determined, and biologically active GRFT was subsequently produced by expression of a corresponding DNA sequence in Escherichia coli. Both native and recombinant GRFT displayed potent antiviral activity against laboratory strains and primary isolates of T- and M- tropic HIV-1 with EC50 values ranging from 0.043 to 0.63 nM. GRFT also aborted cell-to-cell fusion and transmission of HIV-1 infection at similar concentrations. High concentrations (e.g. 783 nM) of GRFT were not lethal to any tested host cell types. GRFT blocked CD4-dependent glycoprotein (gp) 120 binding to receptor-expressing cells and bound to viral coat glycoproteins (gp120, gp41, and gp160) in a glycosylation-dependent manner. GRFT preferentially inhibited gp120 binding of the monoclonal antibody (mAb) 2G12, which recognizes a carbohydrate-dependent motif, and the (mAb) 48d, which binds to CD4-induced epitope. In addition, GRFT moderately interfered with the binding of gp120 to sCD4. Further data showed that the binding of GRFT to soluble gp120 was inhibited by the monosaccharides glucose, mannose, and N-acetylglucosamine but not by galactose, xylose, fucose, N-acetylgalactosamine, or sialic acid-containing glycoproteins. Taken together these data suggest that GRFT is a new type of lectin that binds to various viral glycoproteins in a monosaccharide-dependent manner. GRFT could be a potential candidate microbicide to prevent the sexual transmission of HIV and AIDS. 相似文献
153.
Hirth BH Qiao S Cuff LM Cochran BM Pregel MJ Gregory JS Sneddon SF Kane JL 《Bioorganic & medicinal chemistry letters》2005,15(8):2087-2091
A series of 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid diamides that increase chloride transport in cells expressing mutant cystic fibrosis transmembrane conductance regulator (CFTR) protein has been identified from our compound library. Analoging efforts and the resulting structure-activity relationships uncovered are detailed. Compound potency was improved over 30-fold from the original lead, yielding several analogs with EC(50) values below 10nM in our cellular chloride transport assay. 相似文献
154.
Nonrandom location of IS1 elements in the genomes of natural isolates of Escherichia coli 总被引:2,自引:0,他引:2
We have studied the spatial distribution of IS1 elements in the genomes of
natural isolates comprising the ECOR reference collection of Escherichia
coli. We find evidence for nonrandomness at three levels. Many pairs of IS1
elements are in much closer proximity (< 10 kb) than can be accounted
for by chance. IS1 elements in close proximity were identified by
long-range PCR amplification of the genomic sequence between them. Each
amplified region was sequenced and its map location determined by database
screening of DNA hybridization. Among the ECOR strains with at least two
IS1 elements, 54% had one or more pairs of elements separated by < 10
kb. We propose that this type of clustering is a result of "local hopping,"
in which we assume that a significant proportion of tranposition events
leads to the insertion of a daughter IS element in the vicinity of the
parental element. A second level of nonrandomness is found in strains with
a modest number of IS1 elements that are mapped through the use of inverse
PCR to amplify flanking genomic sequences: in these strains, the insertion
sites tend to be clustered over a smaller region of chromosome than would
be expected by chance. A third level of nonrandomness is observed in the
composite distribution of IS elements across strains: among 20 mapped IS1
elements, none were found in the region of 48-77 minutes, a significant
gap. One region of the E. coli chromosome, at 98 min, had a cluster of IS1
elements in seven ECOR strains of diverse phylogenetic origin. We deduce
from sequence analysis that this pattern of distribution is a result of
initial insertion in the most recent common ancestor of these strains and
therefore not a hot spot of insertion. Analysis using long- range PCR with
primers for IS2 and IS3 also yielded pairs of elements in close proximity,
suggesting that these elements may also occasionally transpose by local
hopping.
相似文献
155.
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158.
Synopsis There was partial spatial and complete temporal overlap of spawning by Etheostoma flabellare and E. nigrum in Marsh Creek, Wisconsin. E. flabellare tended to spawn at shallower depths than E. nigrum. Both species spawned over a greater range of depths in an area with few spawning sites (cavities under rocks or logs) than
in an area where spawning sites were abundant. In the laboratory E. flabellare were able to prevent E. nigrum from occupying cavities they would have otherwise occupied. E. nigrum appear to be competitively inferior to E. flabellare in terms of spawning-site acquisition and retention, but possess several attributes that may allow them to persist in the
presence of the latter. 相似文献
159.
The toxicity of synergism of and resistance to insecticides in four strains of German cockroach, Blattella germanica (L.), were investigated. Toxicity of nine insecticides by topical application to the susceptible strain varied greater than 2,000-fold, with deltamethrin (LD50 = 0.004 micrograms per cockroach) and malathion (LD50 = 8.4 micrograms per cockroach) being the most and least toxic, respectively. Resistance to pyrethrins (9.5-fold) in the Kenly strain was unaffected by the synergists piperonyl butoxide (PBO) or S,S,S-tributylphosphorotrithioate (DEF), suggesting that the metabolism is not involved in this case. Malathion resistance in the Rutgers strain was suppressible with PBO, implicating oxidative metabolism as a resistance mechanism. The Ectiban-R strain was resistant to all the pyrethroids tested, and cypermethrin resistance was not suppressible with PBO or DEF. These findings support results of previous studies that indicated this train has a kdr-like mechanism. Bendiocarb resistance in both the Kenly and Rutgers strains was partially suppressed by either PBO or DEF, suggesting that oxidative and hydrolytic metabolism are involved in the resistance. Trends between the effects of the synergists on the susceptible versus resistant strains are discussed. 相似文献
160.
S-100 protein stimulates cellular proliferation 总被引:2,自引:0,他引:2
Judith R. Klein Dave. S. B. Hoon Janet Nangauyan Edward Okun Alistair J. Cochran 《Cancer immunology, immunotherapy : CII》1989,29(2):133-138
Summary S-100 protein (S-100p) is a small, acidic, calcium-binding protein that is present (predominantly) in the cytoplasm of many types of cells including those of neuroectodermal origin, such as glial cells, schwann cells and melanocytes. In human melanoma cells S-100p is abundant relative to the small quantities expressed by normal melanocytes. We investigated the possibility that this protein may be a growth factor. Purified S-100p from bovine brain or human melanoma cells was added exogenously to human melanoma cells and peripheral blood lymphocytes (PBL) and their growth in the presence of different concentrations of S-100p was determined using a [3H]dT-uptake proliferation assay. The growth of melanoma cells was stimulated by S-100p at concentrations of 1.95–31.25 g/ml. Slight inhibition of cell proliferation occurred at high concentrations (125 g/ml). Maximum stimulation of PBL was at 31.25 g/ml. PBL were not inhibited even at high concentrations of S-100p (125 g/ml). PBL stimulation by S-100p did not require the presence of monocytes/macrophages. Though stimulation by S-100p is not restricted to a specific cell type, when released by melanoma cells it may function as an autocrine tumor growth factor. Other cells, such as PBL, coming in contact with S-100p are also stimulated to proliferate. 相似文献