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1.
H. J. Sips H. A. de Wit-Verbeek J. de Wit A. Westerveld H. Galjaard 《Human genetics》1985,69(4):340-344
Summary A series of man-Chinese hamster and man-mouse somatic cell hybrids was investigated to study the localization of the genes coding for the human lysosomal enzyme -galactosidase (EC 3.2.1.23) and for its protective protein. Using a monoclonal antibody, raised against human placental -galactosidase, it was observed that the structural locus for the -galactosidase polypeptide is located on chromosome 3. The nature of the involvement of chromosome 22 in the expression of human -galactosidase was elucidated by metabolic labelling of the hybrids with radioactive amino acids, immunoprecipitation with monoclonal and polyclonal antibodies against -galactosidase, followed by analysis via gel electrophoresis and fluorography.The data show that the presence of chromosome 22 coincides with the presence of a 32 kd protein. This polypeptide, the protective protein was previously shown to be intimately associated with human -galactosidase. In addition, the protective protein was found to be essential for the in vivo stability of -galactosidase by aggregating -galactosidase monomers into high molecular weight multimes. Both chromosome 3 and 22 are therefore necessary to obtain normal levels og -galactosidase activity in human cells. 相似文献
2.
Reinhart Munk 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1968,58(4):423-428
Zusammenfassung Der Verlauf des Nahrungsflusses im Darmtrakt der Kleinzikade Euscelidius variegatus wird nach Verfütterung von farbstoffhaltiger Nährlösung ermittelt. Es wird der Beweis erbracht, daß die aufgenommene Nahrungsmenge in der Filterkammer geteilt wird und die beiden Anteile den Darmtrakt auf zwei verschiedenen Wegen in Richtung Rektalblase passieren. Ein Anteil der aufgenommenen Nährlösung wird über einen Kurzschlußweg in der Filterkammer sowohl über den Filterkammerdarm als auch über die Kryptonephridien direkt in den Enddarm gepumpt, während die in der Magentasche der Filterkammer verbleibenden Nahrungsanteile über einen langen Verdauungsweg zum After gelangen. Hierbei wird der Magentascheninhalt in den Magen gedrückt. Von dort aus passiert er den Mitteldarm und erreicht über den Enddarm den After. Der Kurzschlußweg und der Verdauungsweg können gleichzeitig benutzt werden. Der Kurzschlußweg wird von der Nahrung jedoch in viel kürzerer Zeit durchströmt als der längere Verdauungsweg.
The directions of the flow of food in the alimentary trad of the leafhopper Euscelidius variegatus KBM. (Jassidae)
Summary The leafhopper Euscelidius variegatus is fed with synthetic food, coloured with 1% Azorubin-S. Its flow in the alimentary tract has been studied. It has been found that the sucked-in food is divided into two parts in the filter chamber, each taking different way in the alimentary tract for its flow. One part of the food is pumped into the hindgut via the short circuit way going through the filter chamber once over the Filterkammerdarm and also over the kryptonephries. That part of the food, which remains in the pocket of the filter chamber takes the long digestion way to the anus over stomach, midgut and hindgut. Both the ways could be used at the same time. But the food takes much shorter time for its passage through the short circuit way as compared to the time needed for the long digestion way.相似文献
3.
Yu. V. Verkhovtseva Ya. Yu. Filina D. E. Pukhov 《Journal of Evolutionary Biochemistry and Physiology》2001,37(4):444-450
The paper reviews data summarizing points of view about the conceptual role of iron in the appearance and evolutionary formation of the Earth and its biosphere. Participation of iron and its compounds in the appearance and development of processes of anaero- and aerobiosis as fundamental blocks of metabolism is presented as a hierarchical scheme. Magnetically arrayed iron compounds, in which the element is both in the Fe(II) and in the Fe(III) state, are considered a connecting link between the hierarchical levels. It is shown that the energy transformation Fe(II) Fe(III) is an oxidation–reduction energy core of the most important metabolic iron complexes and of processes of biogenesis both at the cellular level and in biogeosystems. 相似文献
4.
Lothar Diers 《Molecular & general genetics : MGG》1967,100(1):56-62
Summary Up to now Antirrhinum was classified as a typical example for a uniparentalmaternal inheritance of the plastids. However, the findings reported here prove that also the male gametophyte of Antirrhinum may occasionally transmit plastids into the egg. This conclusion is based on genetic experiments involving a form of the plastom mutant prasinizans which is described as gelbgrüne prasinizans. In contrast to all other plastid mutations known in Antirrhinum majus this mutant originated in Sippe 50 is completely viable. In plants containing plastids of this mutant type only, the mutant character is manifested during early growth stages. Cotyledons and first foliage leaves which are initially white or white yellow, slowly turn green and become indistinguishable from normal Sippe 50. Reciprocal crosses of green Sippe 50 with gelbgrüne prasinizans gave few variegated descendants; the others were exclusively plants identical with the maternal parent as far as leaf colour is concerned (Table). The variegated individuals cannot be gene mutants since selfing and crossing experiments showed non-mendelian inheritance. Furthermore it could be ruled out that in the cross Sippe 50 x gelbgrüne prasinizans the three variegated descendants represent spontaneous new plastom mutants because the pale tissue in these plants turned green in the same way as the paternal parent. Because of the typical greening of this mutant and since plastid mutations could be ruled out we have to conclude that plastids were transmitted by the pollen parent into the egg. There these plastids multiplied together with the maternal plastids giving rise to the chimeras after sorting-out of the two plastid types. This interpretation is supported by the observation of mixed cells in tissues where the leaf variegation is finely mosaiced. The results were possible only because the plastids of the pollen parent can be unequivocally recognised. 相似文献
5.
Gabriele Möller Folkert Reck Hans Paulsen Kanwal J. Kaur Mohan Sarkar Harry Schachter Inka Brockhausen 《Glycoconjugate journal》1992,9(4):180-190
UDP-GlcNAc: Man3R 2-N-acetylglucosaminyltransferase I (GlcNAc-T I; EC 2.4.1.101) is the key enzyme in the synthesis of complex and hybrid N-glycans. Rat liver GlcNAc-T I has been purified more than 25,000-fold (M
r 42,000). TheV
max for the pure enzyme with [Man6(Man3)Man6](Man3)Man4GlcNAc4GlcNAc-Asn as substrate was 4.6 µmol min–1 mg–1. Structural analysis of the enzyme product by proton nuclear magnetic resonance spectroscopy proved that the enzyme adds anN-acetylglucosamine (GlcNAc) residue in 1–2 linkage to the Man3Man-terminus of the substrate. Several derivatives of Man6(Man3)Man-R, a substrate for the enzyme, were synthesized and tested as substrates and inhibitors. An unsubstituted equatorial 4-hydroxyl and an axial 2-hydroxyl on the -linked mannose of Man6(Man3)Man-R are essential for GlcNAc-T I activity. Elimination of the 4-hydroxyl of the 3-linked mannose (Man) of the substrate increases theK
M 20-fold. Modifications on the 6-linked mannose or on the core structure affect mainly theK
M and to a lesser degree theV
max, e.g., substitutions of the Man6 residue at the 2-position by GlcNAc or at the 3- and 6-positions by mannose lower theK
M, whereas various other substitutions at the 3-position increase theK
M slightly. Man6(Man3)4-O-methyl-Man4GlcNAc was found to be a weak inhibitor of GlcNAc-T I.Abbreviations BSA
Bovine serum albumin
- Bn
benzyl
- Fuc, F
l-fucose
- Gal, G
d-galactose
- GalNAc, GA
N-acetyl-d-galactosamine
- Glc
d-glucose
- GlcNAc, Gn
N-acetyl-d-glucosamine
- HPLC
high performance liquid chromatography
- Man, M
d-mannose
- mco
8-methoxycarbonyl-octyl, (CH2)8 COOOCH3
- Me
methyl
- MES
2-(N-morpholino)ethanesulfonate
- NMR
nuclear magnetic resonance
- PMSF
phenylmethylsulfonylfluoride
- pnp
p-nitrophenyl
- SDS
sodium dodecyl sulfate
- T
transferase
- Tal
d-talose
- Xyl
d-xylose;
- {0, 2 + F}
Man6 (GlcNAc2Man3) Man4GlcNAc4 (Fuc6) GlcNAc
- {2, 2}
GlcNAc2Man6 (GlcNAc2Man3) Man4GlcNAc4GlcNAc; M5-glycopeptide, Man6 (Man3) Man6 (Man3) Man4 GlcNAc4GlcNAc-Asn
Enzymes: GlcNAc-transferase I, EC 2.4.1.101; GlcNAc-transferase II, EC 2.4.1.143; GlcNAc-transferase III, EC 2.4.1.144; GlcNAc-transferase IV, EC 2.4.1.145; GlcNAc-transferase V, UDP-GlcNAc: GlcNAc2 Man6-R (GlcNAc to Man) 6-GlcNAc-transferase; GlcNAc-transferase VI, UDP-GlcNAc: GlcNAc6(GlcNAc2) Man6-R (GlcNAc to Man) 4-GlcNAc-transferase; Core 1 3-Gal-transferase, EC 2.4.1.122; 4-Gal-transferase, EC 2.4.1.38; 3-Gal-transferase, UDP-Gal: GlcNAc-R 3-Gal-transferase; blood group i 3-GlcNAc-transferase, EC 2.4.1.149; blood group I 6-GlcNAc-transferase, UDP-GlcNAc: GlcNAc3Gal-R (GlcNAc to Gal) 6-GlcNAc-transferase. 相似文献
6.
Unravelling the factors that contribute to the formation and the stability of -sheet structure in peptides is a subject of great current interest. A -hairpin, the smallest -sheet motif, consists of two antiparallel hydrogen-bonded -strands linked by a loop region. We have performed a statistical analysis on protein -hairpins showing that the most abundant types of -hairpins, 2:2, 3:5 and 4:4, have characteristic patterns of 13C and 13C conformational shifts, as expected on the basis of their and angles. This fact strongly supports the potential value of 13C and 13C conformational shifts as a means to identify -hairpin motifs in peptides. Their usefulness was confirmed by analysing the patterns of 13C and 13C conformational shifts in 13 short peptides, 10–15 residues long, that adopt -hairpin structures in aqueous solution. Furthermore, we have investigated their potential as a method to quantify -hairpin populations in peptides. 相似文献
7.
K. Sankara Rao 《Plant cell reports》1988,7(7):546-549
Rapid multiplication of axillary meristems and direct shoot development occurred from nodal explants of mature Eucalyptus tereticornis Sm. with 5.3 M NAA, 1.1 M IAA and 4.4 M BA in Murashige-Skoog medium. Repeated subcultures of the second generation shoot cultures into low cytokinin-auxin containing media (0.44–0.88 M BA+0.1 M NAA) yielded axillary microshoots in large numbers. Half-strength MS liquid medium with 4.9 M IBA, 5.5 M IAA and 5.3 M NAA for four days, half-strength semi-solid hormonefree MS medium with charcoal, and MS liquid medium without charcoal and hormones, in sequence, induced rooting of shoots in the dark. This system is suitable for the mass propagation of this difficult-to-root eucalypt.Abbreviations BA
6-benzyladenine
- IAA
indole-3-acetic acid
- IBA
-indole-3-butyric acid
- 2-iP
isopentyl adenine
- Kn
kinetin
- MS
Murashige-Skoog
- NAA
-naphthalene acetic acid
- PVP
polyvinylpyrrolidone 相似文献
8.
Summary Suspensions of endocrine pancreas cells were prepared by shaking collagenase-isolated rat islets of Langerhans in calcium-free buffer. When incubated with 1.0 mM substrate at pH 7.4, the cells split,P
i from 5-AMP at a rate of 87 nmol/h per g DNA, and from-glycerophosphate at a rate of 25 nmol/h per g DNAK
m for 5 AMP was about 54 M. Adenosine or theophylline inhibited the 5-AMP hydrolysis. Homogenization of the cells increased the activity toward 5-AMP by 23% and that toward-glycerophosphate by 115%. Injecting rats with cortisone had no effect on the 5-AMP hydrolysis by whole cells but significantly increased the activity in cell homogenates; the intracellular activity toward 5-AMP was more than doubled by the cortisone treatment. Staining whole islet cells for 5-AMP-splitting activity resulted in a demarcation of the cell periphery in control rats. Cells from cortisone-treated rats showed heavier deposits of reaction product, and their cell periphery did not stand out as clearly. It is suggested that 5-nucleotidase is largely an ectoenzyme in normal rat islet cells. The cells also contain an as yet unidentified intracellular phosphatase that seems to be solely responsible for the increased hydrolysis of 5-AMP in cortisone-treated rats. 相似文献
9.
Cary Willard Elsie Wong John F. Hess Che-Kun James Shen Barbara Chapman Allan C. Wilson Carl W. Schmid 《Journal of molecular evolution》1985,22(4):309-315
Summary The DNA base sequences of the entire chimpanzee 1 globin gene and an additional 1 kb of DNA flanking both the human and chimpanzee genes have been determined. Whereas the human 1 gene contains a termination codon in the sixth position, the chimpanzee gene appears to be functional. This finding confirms Proudfoot et al.'s suggestion that the human 1 gene was recently inactivated. Like the corresponding human 1 and 2 genes, the first and second introns of the chimpanzee 1 gene are occupied largely by tandem repeats of short oligonucleotides. These tandem repeats have undergone several rearrangements since the divergence of the human and chimpanzee 1 genes. 相似文献
10.
Marilyn K. Nations Linda A. Camino Frederic B. Walker 《Culture, medicine and psychiatry》1985,9(3):223-240
This study documents that ethnomedical beliefs and practices play an important role in primary care in a southern community. Thirty-three of 73 patients from a rural Appalachian area coming to a university primary care internal medicine practice presented 54 ethnomedical complaints such as high blood (24.1%), Weak 'n dizzy (22.2%), nerves (16.7%), sugar (5.6%) and fallin' out (3.7%). Thirty-three patients had both biomedical and ethnomedical complaints, 40 patients had biomedical complaints without ethnomedical complaints and no patients presented with ethnomedical complaints alone. Over two-thirds of all patients consulted non-medical personnel for their complaints, mostly family and friends, and 70 percent self-treated prior to clinic consultation. Patients presenting with ethnomedical complaints when compared with those presenting with biomedical complaints sought advice of non-physicians significantly more often (p < 0.02); no statistical difference, however, was found in their self-treatment practices. Ninety-two of 130 biomedical complaints were recorded by the patient's physician but none of the 54 ethnomedical complaints were formally recorded (p < 0.001). The high incidence of ethnomedical complaints in this population and the failure of physicians to recognize these complaints demand that primary care medicine residents be taught improved history-taking skills and the essentials of ethnomedical illnesses if they are to provide culturally-sensitive patient care. [ethnomedicine; physician education; Southern black and white Appalachian folk medicine; culturally-appropriate primary care.] 相似文献
11.
Junker T 《Journal of the history of biology》1996,29(1):29-77
Conclusion As frequently pointed out in this discussion, one of the most characteristic features of Mayr's approach to the history of biology stems from the fact that he is dealing to a considerable degree with his own professional history. Furthermore, his main criterion for the selection of historical episodes is their relevance for modern biological theory. As W. F. Bynum and others have noted, the general impression of his reviewers is that one of the towering figures of evolutionary biology has now written a towering history of his discipline.138 Bynum is here referring to The Growth of Biological Thought, but this observation holds equally true for Mayr's other historical writings: One must surely read this book [One Long Argument] not only for its content in itself, but for what it tells of its author. And certainly as one does so, one comes away full-handed. Many, if not all, of the disputes and controversies that have driven Mayr through his long intellectual life reappear, stated as forcefully and elegantly as ever.139
Up to this point, most reviewers agree; the bone of contention is, rather, how to evaluate Mayr's historical work, considering this observation. The two related characteristics of his work-I will call them subjectivity and presentism-stand in opposition to a widespread approach in the history of science exemplified by Kuhn's suggestion that insofar as possible..., the historian should set aside the science that he knows. His science should be learned from the textbooks and journals of the period he studies.140 There are, however, historians who consider the close connection between Mayr and the subject matter of his historical studies to be an advantage.141
On the other hand, it is assumed that the connection between past and present must result in a distortion of the historical truth and lead to a historiographical fallacy, commonly referred to as Whig history. Herbert Butterfield, who in 1931 gave the term its now generally accepted meaning, believed that real historical understanding is not achieved by the subordination of the past to the present, but rather by our making the past our present and attempting to see life with the eyes of another century than our own142. Unfortunately, Butterfield's definition of what he considers Whig history remains somewhat vague, and modern authors have emphasized what they consider most important. Butterfield's subordination of the past to the present is referred to in respect to the selection of subjects (there are more biographies of Charles Darwin than of, let's say, Louis Agassiz),143 to the evaluation of historical authors,144 or, more generally, to all kinds of histories with one eye, so to speak, upon the present.145 The underlying tendency of Whig historians is to produce a historical account told from the viewpoint of those in power,146 leading to a glorification of the present.147 It is obvious that Mayr's strongly presentist approach to the history of biology can be called Whiggish, if we apply the criteria of selection or reference. However, it might be worth mentioning that the program of writing a strictly historicist account of the history of science is challenged by various authors.148 For Mayr, it is not only legitimate but necessary to compare the present situation with the past. Whiggish is only the evaluation of an author in terms of our time.149
I cannot discuss the Whit/anti-Whig controversy in any detail here, apart from saying that Mayr has defended himself rather extensively against the charges of being Whiggish.150 Nevertheless, it may be useful to touch on some of the criticisms that are predominant in reviews of his writings. First, we encounter the notion that historians can write a true and convincing historical account only if they have no personal interest or interpretation of their own; Mayr, on the other hand, because he has such strong interpretations of his own, ... cannot possibly convince everyone that he is right about everything.151 It makes one wonder, what historian has ever been able to convince everyone that he or she is right about everything? But apart from this peculiar idea, it unquestionably poses certain dangers if the subject matter of historical scrutiny and the author are identical. At the same time, this identity brings certain advantages with it, especially firsthand experiences of the period in discussion. Whether these personal memories ultimately result in a distorted picture of the past has to be decided in every particular instance. The notion that a scientific study can be conducted by a completely detached observer from a neutral standpoint has been shown to be impossible in physics, and it is also an illusion in historiography. The question is not whether, but which kind of interest are the underlying motivation for a historian. At this point, Mayr is ahead of his critics when he suggests that our understanding of the past always has a subjective component: The main reason, however, why histories are in constant need of revision is that at any given time they merely reflect the present state of understanding; they depend on how the author interpreted the current zeitgeist of biology and on his own conceptual framework and background. Thus, by necessity the writing of history is subjective and ephemeral.152
Second, the temporal proximity between the event and the historical analysis makes difficulties inevitable and will finally result in certain false assessments. But this applies to all historians when they discuss recent problems, regardless of whether they are personally involved or not: As long as the battle between Darwinism and Lamarckism was raging, it was quite impossible to undertake an unbiased evaluation of Lamarck. ...[The] definite refutation of Lamarck's theory of evolutionary causation clears the air. We can now study him without bias and emotion and give him the attention that this major figure in the history of biology clearly deserves.153
Third, Mayr is primarily interested in biological problems and not, for instance, historiographical, sociological, or psychological questions. Several authors have remarked that since the beginning of the professionalization of the history of science in the 1960s, a rift between two groups has developed, resulting from the heterogeneous professional backgrounds and interests of the people involved: the authors who were originally biologists and became interested in the history of their discipline only later on, and the authors who were trained as historians.154 Whereas the first group, the biologists, tend to be laymen in history proper, the historians are in most cases laymen in biology. Different professional backgrounds obviously shape the historical perspective in both groups, but neither approach is necessarily superior. The great number of important books in the history of biology written by biologist documents how valuable this point of view can be. On the other hand, it cannot be denied that the writings of biologists in the history of science tend to have a strong internalist tendency and often neglect the professional, cultural, and political context of science. Mayr's approach is that of a biologist; it is internalist, and typical for scientists who turn to the history of their discipline.I want to conclude my analysis with a quotation from a review by Douglas J. Futuyma, which gives a perceptive glimpse of Mayr's personality and style: One cannot help standing in awe of the germanic capacity for vast, allembracing synthesis: consider the lifelong devotion of Goethe to Faust, or Wagner's integration of the arts into a Gesamtkunstwerk in which all of human history and experience is wrought into epic myth. It is perhaps in this tradition that Ernst Mayr's The Growth of Biological Thought stands: a history of all of biology, a Ring des Nibelungen complete with leitmotivs such as the failures of reductionism, the struggle of biology for independence from physics, and the liberation of population thinking from the bounds of essentialism.155 Within this style of thinking Mayr has to offer...nothing less than a vision of biology that places neodarwinian evolutionary theory firmly at the centre.156 There may be other visions of biology, but few of them have as indefatigable and able representatives as Darwinism has in Ernst Mayr. 相似文献
12.
Studies on the sites expressing evolutionary changes in the structure of eukaryotic 5S ribosomal RNA
Guo-rong Qi Gong-jie Cao Peng Jiang Xiao-li Feng Xiang-rong Gu 《Journal of molecular evolution》1988,27(4):336-340
Summary We have determined the complete sequences of 5S rRNAs from a lamprey (Lampetra reissneri), a lancelet (Branchiostoma belcheri), silkworms (Philosamia cynthia ricini, Bombyx mori, Antheraea pernyi), and a silkworm hybrid (artificially fertilized hybrid species ofPhilosamia cynthia ricini x Bombyx mori ), as well as those of cotton seeds (Gossypium hirsutum L.). Having compared more than 170 eukaryotic 5S rRNAs of which seven sequences have been determined by our group as mentioned above, we have found that the evolutionary sites that exist at special locations in these structures are closely related to the evolution of eukaryotes. The changes proceed step by step in an orderly way, i.e., the change in nucleotide residues of the evolutionary sites depends on the order of the evolution of the species and shows group-specific patterns. 相似文献
13.
Although a -turn consists of only four amino acids, it assumes many different types in proteins. Is this basically dependent on the tetrapeptide sequence alone or is it due to a variety of interactions with the other part of a protein? To answer this question, a residue-coupled model is proposed that can reflect the sequence-coupling effect for a tetrapeptide in not only a -turn or non--turn, but also different types of a -turn. The predicted results by the model for 6022 tetrapeptides indicate that the rates of correct prediction for -turn types I, I, II, II, VI, and VIII and non--turns are 68.54%, 93.60%, 85.19%, 97.75%, 100%, 88.75%, and 61.02%, respectively. Each of these seven rates is significantly higher than
= 14.29%, the completely randomized rate, implying that the formation of different -turn types or non--turns is considerably correlated with the sequences of a tetrapeptide. 相似文献
14.
The degradation of amyloid beta as a therapeutic strategy in Alzheimer's disease and cerebrovascular amyloidoses 总被引:5,自引:0,他引:5
The deposition of 4-kDa amyloid peptide in the brain is a prominent feature of several human diseases. Such process is heterogeneous in terms of causative factors, biochemical phenotype, localization and clinical manifestations. Amyloid accumulates in the neuropil or within the walls of cerebral vessels, and associates with dementia or stroke, both hereditary and sporadic. Amyloid is normally released by cells as soluble monomeric-dimeric species yet, under pathological conditions, it self-aggregates as soluble oligomers or insoluble fibrils that may be toxic to neurons and vascular cells. Lowering amyloid levels may be achieved by inhibiting its generation from the amyloid -precursor protein or by promoting its clearence by transport or degradation. We will summarize recent findings on brain proteases capable of degrading amyloid with a special focus on those enzymes for which there is genetic, transgenic or biochemical evidence suggesting that they may participate in the proteolysis of amyloid in vivo. We will also put in perspective their possible utilization as therapeutic agents in amyloid diseases. 相似文献
15.
The activity of UDP-Gal: LacCer galactosyltransferase in human placenta was studied by using crude homogenate and Triton CF-54 extract as the source of enzyme. Transfer of galactose to lactosylceramide was optimal in the presence of 0.1% Triton CF-54 and Mn2+ at pH 6.3, and the reaction product was susceptible to -galactosidase.Abbreviations LacCer
lactosylceramide (Gal1-4Glc1-1Cer)
- Gb3
globotriaosylceramide (Gal1-4Gal1-4Glc1-1Cer)
- Gb4
globoside (GalNAc1-3Gal1-4Gal1-4Glc1-1Cer)
- TLC
thin-layer chromatography
- GC/MS
gas chromatography/mass spectrometry
- NMR
nuclear magnetic resonance
- EDTA
ethylenediamine tetraacetic acid
- CHAPS
3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate 相似文献
16.
Summary A feature extractor for a pattern recognizer which can effectively process curvilinear drawings has been synthesized and simulated on a digital computer.The design of the network was suggested by the visual system of higher animals — especially the structure of the receptive fields of cortical neurons. This feature extractor is a multilayered parallel network composed of analog threshold elements. It consists of six layers in cascade. The first layer is a two-dimensional array of photoreceptors. The second layer is a contrast-detecting layer, each element of which has an on-center-type receptive field. The third one is a line-detecting layer. An element of this layer corresponds to a simple cortical cell, and responds to lines whose orientation is proper for the element. Each element has a receptive field consisting of an elongated excitatory region flanked on either side by inhibitory regions. The fourth layer is also a line-detecting layer, but each element, which corresponds to a complex cell, is not sensitive to the exact position of the line. An element of the fifth layer, which may correspond to a hypercomplex cell, responds when the line detected in the preceeding layer is curved. In the final layer, the curvature of the line is detected regardless of the orientation of the line, that is, an element of this layer gives an output approximately proportional to the curvature of the line presented in its receptive field. 相似文献
17.
C. A. Mannella A. F. Neuwald C. E. Lawrence 《Journal of bioenergetics and biomembranes》1996,28(2):163-169
The mitochondrial channel VDAC is presumed to fold as a -barrel although the number and identity of transmembrane -strands in the protein are controversial. Previously, a novel multiple alignment algorithm called the Gibbs sampler was used to detect a residue-frequency motif in sequences of bacterial outer-membrane proteins that corresponds to transmembrane -strands in bacterial porins of known structure (Neuwaldet al., 1995,Protein Science,4, 1618. In the present study, this bacterial motif has been used to screen sets of mitochondrial membrane protein sequences, with matches occurring in only two classes of proteins: VDACs and the outer-membrane protein import pore (ISP42, MOM38). These results suggest a structural (and perhaps evolutionary) relatedness between the bacterial and mitochondrial pore proteins, with the mitochondrial subsequences that match the bacterial motif corresponding to transmembrane -strands as in the porins. 相似文献
18.
Kasheverov IE Zhmak MN Maslennikov IV Utkin YN Tsetlin VI 《Neurochemical research》2003,28(3-4):599-606
Comparative structure-function studies have been carried out for -conotoxin GI acting on nicotinic acetylcholine receptors (AChR) from mammalian muscles and from the electric organ of the Torpedo californica ray and for -conotoxin ImI, which targets the neuronal a7 AChR. A series of analogs has been prepared for this purpose: chemically modified derivatives, including a covalently linked dimer of GI, as well as analogs wherein one or several amino acid residues have been changed using solid-phase peptide synthesis. The activity of all compounds was assessed in competition with radioiodinated and/or tritiated -conotoxin GI for binding to the membrane-bound AChR of Torpedo californica. Binding of radioiodinated -conotoxin GI dimer was also monitored directly, revealing the largest, as compared to all other analogues, difference in the affinity between the two binding sites in the receptor (KD 11 and 1200 nM). Comparison of binding data with the results of CD measurements point to important role of the spatial organization of the -conotoxin second loop in manifestation of their muscle or neuronal specificity. 相似文献
19.
Bart Voorzanger 《Acta biotheoretica》1987,36(1):23-34
Biology cannot accommodate all aspects of culture. Aspects of culture that a biological approach can take into account can be covered by the biological categories of phenotype and environment. There is no need to treat culture as a separate category. Attempts to elaborate biological explanations of cultural variation will meet with success only if biologists expand theories of development, and integrate them in evolutionary biology. The alternative — elaborating the idea of so-called cultural inheritance — makes little sense from a biological point of view. 相似文献
20.
An extensive phylogenetic analysis of the nicotinic-acetylcholine-receptor subunit gene family has been performed by cladistic and phenetic methods. The conserved parts of amino acid sequences have been analyzed by CLUSTAL V and PHYLIP software. The structure of the genes was also taken in consideration. The results show that a first gene duplication may have occurred before the appearance of Bilateria. Three subfamilies then appeared: I-the neuronal -bungarotoxin binding-site subunits (7, 8); III-the neuronal nicotinic subunits (2–6, 2–4), which also contain the muscle acetylcholine-binding subunit (1); and IV—the muscle non- subunits (1, , ). The Insecta subunits (subfamily II) could be orthologous to family III and IV. Several tissular switches of expression from neuron to muscle and the converse can be inferred from the extant expression of subunits and the reconstructed trees. The diversification of the neuronal nicotinic subfamily begins in the stem lineage of chordates, the last duplications occurring shortly before the onset of the mammalian lineage. Such evolution parallels the increase in complexity of the cholinergic systems.Abbreviations -Bgt
-bungarotoxin
- ACh
acetylcholine
- MP
maximum of parsimony
- MYA
million years ago
- NJ
neighbor-joining
- nAChR
nicotinic acetylcholine receptor
Correspondence to: N. Le Novère 相似文献