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51.
Aspergillus flavus grown on yeast extract-sucrose medium produced higher amounts of aflatoxin B1 in the presence of 0.025% sorbic acid than without this chemical with a maximum at 17 days of incubation. Addition of 0.05 to 0.0125% sorbic acid stimulated T-2 toxin production of Fusarium acuminatum cultures grown on maize meal. The highest amounts of the mycotoxin were detected in 14-day-old cultures containing 0.025% sorbic acid. It is assumed that certain amounts of sorbic acid near the minimal inhibitory concentration reduce the activity of the tricarboxylic acid cycle; this may lead to an accumulation of acetyl coenzyme A, which is an essential intermediate in the biosynthesis of aflatoxin B1 and T-2 toxin. 相似文献
52.
Retinotopy and orientation columns in the monkey: A new model 总被引:2,自引:0,他引:2
A model is presented in which orientation columns arise directly out of retinotopy. According to the model, iso-orientation lines are arrayed radially around nodal centers which correspond to cytochrome oxidase patches. The nodal centers form a square matrix superimposed upon the map of ocular dominance stripes. In the supragranular layers horizontal iso-orientation lines run down the centers of ocular dominance stripes, with vertical iso-orientation lines crossing perpendicularly. Diagonal orientations (45 degrees and 135 degrees) are represented as alternating iso-orientation zones at the centers of the interstices in the matrix (internodal centers). Preferred orientations in the infragranular layers are reversed with respect to the supragranular layers. The model is consistent with new data concerning ocularity and preferred orientation in systematic penetrations through striate cortex, and helps to explain some previously puzzling features of the relationship between ocular dominance columns, orientation columns and retinotopy. 相似文献
53.
Cell culture density as a modulator of collagenase expression in normal human fibroblast cultures 总被引:5,自引:0,他引:5
E. A. Bauer 《Experimental cell research》1977,107(2):269-276
The effect of various stages of normal cell growth on human fibroblast collagenase found in the culture medium was studied, so that the regulatory mechanisms of synthesis, secretion and activity of the enzyme could be established. Specific activity of collagenase increased 6- to 10-fold shortly after confluence was reached when compared with low density levels and decreased in post-confluent cultures, suggesting that synthesis and/or release of the enzyme changes with culture density. To assess this possibility, culture medium was examined for immunoreactive collagenase protein by radioimmunoassay. After confluence was reached, immunoreactive collagenase had increased approx. 2-fold, indicating greater secretion, and probably synthesis, of the enzyme. However, the increase in specific activity of the enzyme observed shortly after confluence was greater than could be accounted for by an increase in immunoreactive enzyme protein. As a result of the disproportionate increase in collagenase activity, the collagenase activity per unit immunoreactive protein was also found to be greatest shortly after confluence and decreased in post-confluent cultures. This density-associated modulation of collagenase expression could be reproduced by initiating the cultures at high density after subculture. Expression of collagenase activity was dependent upon intact protein synthetic mechanisms, since cultures maintained in the presence of cycloheximide failed to secrete collagenase into the culture medium. 相似文献
54.
Secretion, subcellular localization and metabolic status of inorganic pyrophosphate in human platelets. A major constituent of the amine-storing granules. 总被引:1,自引:1,他引:0 下载免费PDF全文
The platelet content of PPi is 1.90 +/- mumol/10(11) platelets (S.E.M., n = 19) or about 10.5 nmol/mg of protein, several hundred times that found for rat liver. Some 80% of this PPi is secreted by platelets treated with thrombin with a time course and dose-response relationship similar to secretion of ATP, ADP and 5-hydroxytryptamine (serotonin) from the platelet dense granules. During platelet aggregation induced by ADP and adrenaline, substantial amounts of PPi were secreted, but no release of acid hydrolases was observed. Subcellular-fractionation studies showed that the PPi is highly enriched in the same fraction that contains the storage organelles which store ATP, ADP, Ca2+ and 5-hydroxytryptamine. Inorganic pyrophosphatase was present mainly in the soluble fraction and in the mitochondria. Secretion studies done with platelets prelabelled with [32P]Pi showed that the sequestered PPi was relatively metabolically inactive, as is the ATP and ADP in the storage organelles. The possible participation of PPi in the formation of a bivalent-cation-nucleotide complex associated with amine storage is discussed. 相似文献
55.
56.
Characteristics of single chemoreceptive units sensitive to amino acids and related substances in the crayfish leg 总被引:2,自引:0,他引:2
Ulrike Bauer J. Dudel H. Hatt 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1981,142(1):67-74
Summary Impulses in single afferent fibres from amino acid receptors were recorded extracellularly. Doseresponse relations were determined for different superfused amino acids; the relations all had a slope of 1, a common saturation level, and the action of different amino acids was characterized by a specific half saturation concentration,K
M. The most effective amino acids were always L-serine, L-alanine and L-histidine, having aK
M of 10–5, 2·10–5 and 1.5·10–4 mol/l, respectively. The sequence of effective amino acids was the same for all units tested. Structural requirements for optimal stimulatory action of the amino acid molecules were concluded.Abbreviation
vH
van Harreveld solution
This work was supported by the Deutsche ForschungsgemeinschaftWe gratefully acknowledge assistance in electronics from Mr. W. Zeitz, and in mechanics from Mr. D. Beyer and Mr. L. Müller. Technical help was provided by Mrs. E. Köster, secretarial help by Mrs. L. Bauer. 相似文献
57.
Replicating molecules of three small plasmids, pSM1, pSM2, and pSM3, were isolated from a CsCl density gradient containing ethidium bromide. These plasmids are all derived from R12, a mutant of NR1 (same as R100). By means of pulse-labeling experiments, the replicating forms were located at buoyant densities intermediate between those of the closed circular and open circular DNA bands. These molecules were analyzed by electron microscopy following digestion with restriction endonucleases. Digestion of pSM2 with EcoR1 and with HindIII revealed the presence of a single origin of replication located 1.72 kilobases (kb) from the EcoR1 cutting site (2.04 kb from the HindIII cutting site). These experiments also demonstrated that replication occurs in a unidirectional mode from the origin. Analysis of EcoR1-cleaved replicating molecules of pSM1 and pSM3, which carry common sequences completely or partly homologous to pSM2, provides further evidence for the unidirectional replication of these plasmids from a common origin. The site of the origin of replication was fixed at 85.5 on the kilobase map of R100. This origin, which is located in the RTF region, probably corresponds to one of the replication origins of R100. 相似文献
58.
Physical properties and gel electrophoresis behavior of R12-derived plasmid DNAs. 总被引:21,自引:9,他引:12 下载免费PDF全文
A series of closed circular (I) plasmid DNAs has been derived from drug resistance factor R12, and the nicked circular (II) and linear (III) derivatives of these molecules prepared by irradiation in the presence of ethidium bromide and by treatment with restriction enzyme EcoRI, respectively. These DNAs encompass the molecular weight range 3.6 to 61 megadaltons. The base compositions range from 45% to 51% (GC) as estimated by buoyant density determinations. The smaller plasmids are significantly less supercoiled (9-10%) than are the larger (12-13%). The gel electrophoretic behavior of the three DNA structural forms was determined as a function of molecular weight in agarose gels of concentrations ranging from 0.7% to 1.6% and at electrophoresis salt concentrations from 0.02 M to 0.08 M sodium acetate. The mobilities of DNAs I and III undergo a reversal relative to each other at a molecular weight which decreases with increasing agarose gel concentration. The molecular weight at which DNA II fails to enter a gel depends upon the ionic strength during electrophoresis but not upon the gel concentration. 相似文献
59.
Harold R. Bauer 《Primates; journal of primatology》1977,18(4):913-921
An adult male chimpanzee in the natural habitat has been observed to walk predominantly bipedally after a total forelimb paralysis
in 1966. The major differences from previously described bipedal chimpanzee gait are (1) one third of the femoral extension
is posterior to the hip joint in propulsion, (2) excursion of the swinging foot is close to midline, due to adduction of the
lower hindlimb in swing and propulsive phases, (3) depressed pelvic tilt is on the side of the swinging limb, (4) thoracic
vertebrae rotate and are vertical and erect, and (5) there is only a moderate lateral sway of the midline. This locomotory
complex is interpreted as individual variability and suggests an evolutionary model for the origin of hominid bipedal locomotion. 相似文献
60.
Net charge and oxygen affinity of human hemoglobin are independent of hemoglobin concentration 下载免费PDF全文
G Gros H S Rollema W Jelkmann H Gros C Bauer W Moll 《The Journal of general physiology》1978,72(6):765-773
The dependence of net charge and oxygen affinity of human hemoglobin upon hemoglobin concentration was reinvestigated. In contrast to earlier reports from various laboratories, both functional properties of hemoglobin were found to be independent of hemoglobin concentration. Two findings indicate a concentration-independent net charge of carbonmonoxy hemoglobin at pH 6.6: (A) The pH value of a given carbonmonoty hemoglobin solution remains constant at 6.6 when the hemoglobin concentration is raised from 10 to 40 g/dl, indicating that there is no change in protonation of titratable groups of hemoglobin: (b) the net charge of carbonmonoxy hemoglobin as estimated from the Donnan distribution of 22Na+ shows no dependence on hemoglobin concentration in this concentration range. The oxygen affinity of human hemoglobin was determined from measurements of oxygen concentrations in equilibrated samples using a Lex-O2-Con apparatus (Lexington Instruments, Waltham, Mass.). P50 averaged 11.4 mm Hg at 37 degrees C, pH = 7.2, and ionic strength approximately 0.15. Neither P50 nor Hill's n showed any variation with hemoglobin concentrations increasing from 10 to 40 g/dl. 相似文献