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1.
LiCl treatment releases a nickase implicated in genetic transformation of Streptococcus pneumoniae. 总被引:1,自引:0,他引:1 下载免费PDF全文
When cells competent for genetic transformation of Streptococcus pneumoniae which could bind and enable entry of extracellular DNA molecules were treated with LiCl, they released a nickase that introduced nicks into a double-stranded DNA in the presence of EDTA. The nickase was specific for competent cells and coupled with DNA-binding activity. Furthermore, when noncompetent cells were treated with LiCl, they released the putative receptors for the competence activator. 相似文献
2.
Summary Distribution of molluscan cardio-excitatory tetrapeptide Phe—Met—Arg—Phe—NH2 (FMRFamide) was determined by means of immunohistochemistry in the brain and neurohypophysis of the lamprey, Lampetra japonica. Many FMRFamide-like immunoreactive neurons were found in the periventricular nuclear region and in a region near the mammillary recess. Neurons situated in the former region were larger. The immunoreactive cell groups were shown to be located at sites differing from those of the AF-positive cell groups. The fibers of immunoreactive neurons extended in all directions within the brain and towards the spinal cord, some reaching the third ventricle and capillaries. Thus, FMRFamide-like immunoreactive peptides appear to function as neurotransmitters or neuromodulators and possibly also as neurohormones. FMRFamide-like immunoreactive material was rarely observed in the posterior neurohypophysis (neural lobe), but was noted to be present to a limited extent in the caudal part of the anterior neurohypophysis (median eminence). It would thus follow that FMRFamide-like immunoreactive neurons may not necessarily be related to the hypothalamo-neural lobe system, but may possibly be associated with the hypothalamoadenohypophysial system. The pineal body showed no FMRFamide-like immunoreactivity. 相似文献
3.
Molecular cloning and sequence analysis of cDNA for human hepatocyte growth factor 总被引:62,自引:0,他引:62
K Miyazawa H Tsubouchi D Naka K Takahashi M Okigaki N Arakaki H Nakayama S Hirono O Sakiyama K Takahashi 《Biochemical and biophysical research communications》1989,163(2):967-973
Amino acid sequences of four peptide fragments of human hepatocyte growth factor purified from the plasma of patients with fulminant hepatic failure were determined. Based on the amino acid sequence of one of the fragments, two oligodeoxyribonucleotide mixtures were synthesized and used to screen a human placenta cDNA library. On the screening, two overlapping cDNA clones for human hepatocyte growth factor were isolated and the nucleotide sequence of the cDNA was determined. The entire primary structure of the protein was deduced from the sequence. The protein consists of 728 amino acid residues, including a possible signal peptide at the N-terminus. The sequence revealed that the heavy and light chains which comprise the protein are encoded by the same mRNA and are produced from a common translation product by proteolytic processing. 相似文献
4.
The denaturation of bacteriorhodopsin by various organic solvents was studied using absorption, circular dichroism (CD) and fluorescence measurements. Organic solvents with a hydrogen-bonding group caused the release of retinal. The CD measurements showed that the helical structure was maintained even in the denatured state, whereas its tertiary structure was destroyed. The change in fluorescence intensity of tryptophan and fluorescent retinal also confirmed that the tertiary structure was destroyed. Comparison of the denaturation efficiency of various organic solvents showed that the concentration at denaturation was inversely proportional to the partition coefficient of the denaturant. This inverse proportionality clearly indicated that denaturation was determined by the concentration of denaturants which partitioned into the hydrophobic region of the membrane. It was discussed from the experimental results that the tertiary structure of bacteriorhodopsin was stabilized by the hydrogen-bonding networks between side chains of the helices. The results obtained from analysis of the amino acid sequence were also consistent with the hydrogen-bonding mechanism for the formation of the tertiary structure. 相似文献
5.
The incremental responses from the second-order neurons of the ocellus of the cockroach, Periplaneta americana, have been measured. The stimulus was a white-noise-modulated light with various mean illuminances. The kernels, obtained by cross-correlating the white-noise input against the resulting response, provided a measure of incremental sensitivity as well as of response dynamics. We found that the incremental sensitivity of the second-order neurons was an exact Weber-Fechner function; white-noise-evoked responses from second-order neurons were linear; the dynamics of second-order neurons remain unchanged over a mean illuminance range of 4 log units; the small nonlinearity in the response of the second-order neuron was a simple amplitude compression; and the correlation between the white-noise input and spike discharges of the second-order neurons produced a first-order kernel similar to that of the cell's slow potential. We conclude that signal processing in the cockroach ocellus is simple but different from that in other visual systems, including vertebrate retinas and insect compound eyes, in which the system's dynamics depend on the mean illuminance. 相似文献
6.
Slow and spike potentials were recorded from single cells in the receptor layer of the compound eye of the drone of the honeybee. From electron microscopic observation of the drone ommatidium, it was concluded that the response had been recorded from the retinula cell. The following hypothesis is suggested for the initiation of spike potentials in the drone compound eye: Photic stimulation results in a decrease in the resistance of all or part of the retinula cell membrane, giving rise to the retinal action potential. The retinal action potential causes outflow of the current through the proximal process of the cell. This depolarizing current initiates spike potentials in the proximal process or axon of the retinula cell which are recorded across the soma membrane of the retinula cell. 相似文献
7.
The Development of the Rhabdom and the Appearance of the Electrical Response in the Insect Eye 总被引:4,自引:2,他引:2 下载免费PDF全文
Electron microscopic studies on the development of the rhabdom in the compound eye of the silkworm moth and pupa (Bombyx mori) were carried out in parallel with the recording of the electrical response to photic stimulation. No electrical response to photic stimulation was recorded from the pupal compound eye which had no trace of differentiation of the rhabdom. With the differentiation of development of the rhabdom in the pupal compound eye, electrical responses could be recorded, and the amplitude of such electrical responses increased with the progress of development of the rhabdom. These observations suggest that the rhabdom is probably the site of the photochemical reaction which leads to the generation of the slow retinal action potentials. 相似文献
8.
Effects of monovalent cations and some anions on the electrical properties of the barnacle muscle fiber membrane were studied when the intra- or extracellular concentrations of those ions were altered by longitudinal intra-cellular injection. The resting potential of the normal fiber decreases linearly with increase of logarithm of [K+]out and the decrement for a tenfold increase in [K+]out is 58 mv when the product, [K+]out ·[Cl-]out, is kept constant. It also decreases with decreasing [K+]in but is always less than expected theoretically. The deviation becomes larger as [K+]in increases and the resting potential finally starts to decrease with increasing [K+]in for [K+]in > 250 mM. When the internal K+ concentration is decreased the overshoot of the spike potential increases and the time course of the spike potential becomes more prolonged. In substituting for the internal K+, Na+ and sucrose affect the resting and spike potentials similarly. Some organic cations (guanidine, choline, tris, and TMA) behave like sucrose while some other organic cations (TEA, TPA, and TBA) have a specific effect and prolong the spike potential if they are applied intracellularly or extracellularly. In all cases the active membrane potential increases linearly with the logarithm of [Ca++]out/[K+]in and the increment is about 29 mv for tenfold increase in this ratio. The fiber membrane is permeable to Cl- and other smaller anions (Br- and I-) but not to acetate- and larger anions (citrate-, sulfate-, and methanesulfonate-). 相似文献
9.
Katsunobu Yoshioka Nobuo Shimojo Toyofumi Nakanishi Keiichi Naka Kiyoshi Okuda 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1994,655(2)
A sensitive and specific method was developed for measuring medium-chain dicarboxylic acids (adipic and suberic acid) in urine. These acids were extracted from urine with diethyl ether and converted into fluorescent derivatives with 9-anthryldiazomethane, which can be separated by high-performance liquid chromatography. The reproducibility was high and the recovery from urine was above 90%. Urinary concentrations of adipic acid in streptozotocin-induced diabetic rats were significantly higher than those in control rats. In diabetic patients, both adipic acid and suberic acid tended to be high, but not significantly. This method should be useful for measuring dicarboxylic acids in urine 相似文献
10.
The responses of retinal neurons depend on the interaction of both temporal and spatial aspects of a light stimulus. We developed a linear spatiotemporal model of receptor and horizontal cell layers in the catfish retina based on reciprocal interactions between both layers and coupling within each. Horizontal cell transfer properties were measured experimentally using white-noise intensity modulated light spots of different diameters and were compared with analytical predictions based on the model. Good agreement was obtained with a reasonable choice of model space-constants and feedback parameters. Furthermore, the same set of parameter values determined from spot experiments enabled accurate prediction of experimental horizontal cell responses to traveling gratings. The proposed feedback connections from horizontal cells to receptors quicken the time-course of responses in both layers and sharpen receptive fields. 相似文献