Bacteriophage transport was investigated in laboratory column experiments using sandy soil, a controlled field study in a sandy wash, and laboratory experiments using fractured rock. In the soil columns, the phage MS-2 exhibited significant dispersion and was excluded from 35 to 40% of the void volume but did not adsorb. Dispersion in the field was similiar to that observed in the laboratory. The phage f2 was largely excluded from the porous matrix of the two fractured-rock cores studied, coming through 1.2 and 2.0 times later than predicted on the basis of fracture flow alone. Because of matrix diffusion, nonsorbing solutes were retarded by over a factor of three relative to fracture flow. The time for a solute tracer to equilibrate with the porous matrix of 6.5-cm-diameter by 25-cm-long cores was measured in days. Results of both granular-medium and fractured-rock experiments illustrate the inability of a solute tracer to provide estimates for dispersion and effective porosity that are applicable to a colloid. Bacteriophage can be used to better estimate the maximum subsurface transport rate of colloidal contaminants through a porous formation. 相似文献
The effect of poly(ADP-ribose) synthesis on chromatin structure was investigated by velocity sedimentation and electron microscopy. We demonstrate that locally relaxed regions can be generated within polynucleosome chains by the activity of their intrinsic poly(ADP-ribose)polymerase. This relaxation phenomenon is also shown to be NAD dependent and to be correlated with the formation of hyper(ADP-ribosyl)ated forms of histone H1. Evidence is also presented which suggests that hyper(ADP-ribosyl)ated histone H1 is neither released from the relaxed chromatin, nor does it seem to participate in polynucleosomal aggregation. 相似文献
Lincomycin, a chemically new antibiotic effective against Gram-positive organisms, was evaluated in vitro and tested clinically. In vitro testing indicated that lincomycin is especially effective against Staphylococcus aureus. Clinical testing showed that lincomycin was free of toxicity in a series of 18 cases of staphylococcal infection. Of particular interest was its pronounced effectiveness in nine cases of chronic osteomyelitis, one of which was of 15 years'' duration and unresponsive to all other forms of antibiotic and surgical treatment. The only side effect noted was loose stools in the occasional patient. 相似文献
Summary Stimulation of the exocrine pancreas by the secretagogue urecholine causes degranulation of the acinar cells. Under in vivo conditions, this degranulation is not uniform throughout the tissue. Indeed some of the acini are almost completely depleted of their granules while others display the appearance of resting acini. A noticeable feature is that all the cells of the same acinus display a comparable degree of degranulation. Moreover, groups of neighbouring acini seem to respond simultaneously suggesting that the secretory stimulus is propagated from one acinus to the other. In vitro stimulation of dispersed acini also showed that some of the acini are more responsive than others indicating that this phenomenon can not be attributed to accessibility of the secretagogue to its receptor. These observations lead us to the concept that the response of the pancreatic acinar cell is controlled at the level of the acinus. 相似文献
We studied the response of 31 migraine sufferers (20 women, 11 men) to intravenous tyramine (the tyraminedose)pressor response test). Patients were treated either with pacebo tablets or indoramin, and alpha-adrenergic blocking agent, in a double-blind crrossover trial. We found that patients with migraine required significantly less tyramine to increase their cystolic blod pressure by 30 mm Hg when compared with matched controls. Indoramin significantly increased the amount of tyramine needed to raise the systolic blood pressure among migraine suffers and reduced the incidence of posttyramine migraine for m 46% while patients were on placebo tablets to 8% when they were receiveing indoramin. There was no association between tyramine sensitivity and a history of premenstrual or dietary migraine, nor was there a significant difference in the indierenence in the incidence of post-tyramine migrain between men women. We conclude that the intravenous tyramine test may be valuable in assessing migraine suffers who will respond to an alpha-advenergic blocking agent such as indoramin. 相似文献
We have isolated the gene from Saccharomyces cerevisiae encoding an alpha-mannosidase of unique specificity which catalyzes the removal of one mannose residue from Man9GlcNAc to produce a single isomer of Man8GlcNAc (Jelinek-Kelly, S., and Herscovics, A. (1988) J. Biol. Chem. 263, 14757-14763). Amino acid sequence information was obtained and corresponding degenerate oligonucleotide primers were synthesized for polymerase chain reactions on yeast genomic DNA. The labeled polymerase chain reaction products were used to screen a S. cerevisiae genomic library in YEp24, and positive clones of different lengths with similar restriction maps were isolated. A 4.6-kilobase fragment which hybridized with the probes was sequenced. It contained a 1650-base pair open reading frame encoding peptide sequences corresponding to the amino acid sequences of the purified alpha-mannosidase. The gene, designated MNS1, encodes a 549-amino acid polypeptide of calculated molecular size 63,017 Da produced by an mRNA species of approximately 1.7 kilobases. The protein possesses a putative noncleavable signal sequence near its N-terminal region which probably acts as a transmembrane domain. It has three potential N-glycosylation sites and a calcium-binding consensus sequence. Its amino acid sequence is homologous to the recently isolated cDNA from rabbit liver alpha-1,2 mannosidase which can transform Man9GlcNAc to Man5GlcNAc (Moremen, K. W., Schutzbach, J. S., Forsee, W. T., Neame, P., Bishoff, J., Lodish, H. F., and Robbins, P. W. (1990) Glycoconjugate J. 7, 401). Overexpression of the MNS1 gene caused an 8-10-fold increase in specific alpha-mannosidase activity. Disruption of the MNS1 gene resulted in undetectable specific alpha-mannosidase activity but no apparent effect on growth. These results demonstrate that MNS1 is the structural gene for the specific alpha-mannosidase and that its activity is not essential for viability. 相似文献
Plant natural products (PNP) (e.g., secondary vegetal metabolites and their derivatives) have been a productive source of active ingredients for the pharmaceutical industry. The High Throughput Screening of Plant Natural Products (PNP-HTS) with extracts or isolated compounds has shown to be time consuming, expensive, and not as successful as expected. Recently building upon the innovative fragment-based drug discovery (FBDD) a disruptive approach was developed based on PNP. The fragment approach involves elaboration and/or isolation of weakly binding small molecules with molecular weights between 150 and 250 Da. This method is fundamentally different from HTS in almost every aspect (i.e., size of the compound library, screening methods, and optimization steps from hit to lead). Due to their nature, vegetal natural fragments have unique three-dimensional (3D) properties, high Fsp3, low aromaticity, and large chemo-diversities which represent potential opportunities for developing novel drugs. Preliminary results using vegetal natural fragments appear to be a promising and emerging field which offers valuable prospects for developing new drugs.
Previous studies indicated that empty time intervals are better discriminated in the auditory than in the visual modality, and when delimited by signals delivered from the same (intramodal intervals) rather than from different sensory modalities (intermodal intervals). The present electrophysiological study was conducted to determine the mechanisms which modulated the performances in inter- and intramodal conditions. Participants were asked to categorise as short or long empty intervals marked by auditory (A) and/or visual (V) signals (intramodal intervals: AA, VV; intermodal intervals: AV, VA). Behavioural data revealed that the performances were higher for the AA intervals than for the three other intervals and lower for inter- compared to intramodal intervals. Electrophysiological results indicated that the CNV amplitude recorded at fronto-central electrodes increased significantly until the end of the presentation of the long intervals in the AA conditions, while no significant change in the time course of this component was observed for the other three modalities of presentation. They also indicated that the N1 and P2 amplitudes recorded after the presentation of the signals which delimited the beginning of the intervals were higher for the inter- (AV/VA) compared to the intramodal intervals (AA/VV). The time course of the CNV revealed that the high performances observed with AA intervals would be related to the effectiveness of the neural mechanisms underlying the processing of the ongoing interval. The greater amplitude of the N1 and P2 components during the intermodal intervals suggests that the weak performances observed in these conditions would be caused by an attentional bias induced by the cognitive load and the necessity to switch between modalities. 相似文献