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121.
A series of unstable mono- and di-esters of the tetracyclic diterpene ingenol were isolated from the pro-inflammatory ether-soluble fraction of the latex of Euphorbia kamerunica. The esters were isolated by a neutral process involving column and thin-layer chromatography. The monoesters were identified by spectroscopic methods and hydrolysis reactions as ingenol-3-decanoate, ingenol-3-dodecanoate, ingenol-5-hexadienoate and ingenol-5-octenoate and the diesters as 20-acetyl-ingenol-3-octenoate and 20-acetyl-ingenol-3-angelate. 相似文献
122.
Nonrandom mating with respect to color is well documented in the dimorphic Lesser Snow Goose. A set of mathematical models and data from the long-term study at La Pérouse Bay, Manitoba, Canada are used to examine various hypotheses advanced to explain the mechanisms behind the assortative mating. Among the factors considered are mate choice based on familial color, accidental formation of genetically unrelated families, and nonuniform distribution of colors in the region where mate selection occurs. 相似文献
123.
124.
South-Central European fossil hominids dated to the Upper Pleistocene exhibit a distinct morphological and metric continuum in supraorbital form from early Neandertal (Krapina), through late Neandertals (Vindija), to early Upper Paleolithic hominids. The supraorbital morphologies pertinent to this continuum are documented, and the alterations in size and morphology are discussed ralative to the function of supraorbital superstructures and their relationship to overall craniofacial form. It is concluded that this continuum most likely reflects localized transition between Neandertals and modern man in this region of Europe. 相似文献
125.
Genes Affecting the Expression of Cytochrome c in Yeast: Genetic Mapping and Genetic Interactions 总被引:33,自引:4,他引:29
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The four mutant genes, cyc2, cyc3, cyc8 and cyc9, that affect the levels of the two iso-cytochromes c in the yeast Saccharomyces cerevisiae have been characterized and mapped. Both cyc2 and cyc3 lower the amount of iso-1-cytochrome c and iso-2-cytochrome c; whereas, cyc8 and cyc9 increase the amount of iso-2-cytochrome c. The cyc2, cyc3, cyc8 and cyc9 genes are located, respectively, on chromosomes XV, I, II and III, and are, therefore, unlinked to each other and unlinked to CYC1, the structural gene of iso-1-cytochrome c and to CYC7, the structural gene of iso-2-cytochrome c. While some cyc3 mutants are completely or almost completely deficient in cyotchromes c, none of the cyc2 mutants contained less than 10% of parental level of cytochrome c even though over one-half of the mutants contain UAA or UAG nonsense mutations. Thus, it appears as if a complete block of the cyc2 gene product still allows the formation of a residual fraction of cytochrome c. The cyc2 and cyc3 mutant genes cause deficiencies even in the presence of CYC7, cyc8 and cyc9, which normally cause overproduction of iso-2-cytochrome c. We suggest that cyc2 and cyc3 may be involved with the regulation or maturation of the iso-cytochromes c. In addition to having high levels of iso-2-cytochromes c, the cyc8 and cyc9 mutants are associated with flocculent cells and other abnormal phenotypes. The cyc9 mutant was shown to be allelic with the tup1 mutant and to share its properties, which include the ability to utilize exogenous dTMP, a characteristic flocculent morphology, the lack of sporulation of homozygous diploids and low frequency of mating and abnormally shaped cells of alpha strains. The diverse abnormalities suggest that cyc8 and cyc9 are not simple regulatory mutants controlling iso-2-cytochrome c. 相似文献
126.
The concepts of elasticity, invulnerability and invadability 总被引:2,自引:0,他引:2
Users of mathematical models in ecological research have emphasized mathematical elegance in elucidating the dynamics of ecosystem models with fixed collections of state variables instead of addressing the equally important question of what effects a changing ecosystem structure has on the system's dynamics. Our work addresses the effect of invasion on the species composition of communities. In the context of a linear model, we found that as communities were made more complex (in terms of the number of species they contained and the number of interactions among these species) the probability of their being stable decreased, but the probability of their being invulnerable to invasion by other species increased. These results are consistent with the hypothesis that, through time, communities approach an intermediate complexity at which the influences of environmental stochasticity (which tends to destabilize complex communities) and invasion pressure (which tends to add species to simple communities) counterbalance one another. At this intermediate complexity the average rate of change of species composition is low. 相似文献
127.
The sesquiterpene lactones isolated from species in the genus Artemisia have been reviewed in an attempt to better understand the phylogeny and systematics of the four sections (subgenera), Abrotanum, Absinthium, Dracunculus and Seriphidium, proposed by Besser in 1829. The absence of hair on the receptacle is the only morphological characteristic separating species of Abrotanum from the species of Absinthium. There are no chemical characteristics segregating the species in these two subgenera since both produce eudesmanolides and guaianolides that are identical or biosynthetically similar. This suggests that the two subgenera could be combined into one (Artemisia) as proposed by Poljakov. The subgenus Seriphidium is composed of two geographical groups, one in the Old World and the other in the New World. The Old World species almost exclusively produce sesquiterpene lactones in the eudesmanolide class whereas the New World species (section Tridentatae) produce eudesmanolides and guaianolides, many of the latter being identical or structurally related to the sesquiterpene lactones in New World Abrotanum species. The chemical data in conjunction with geographic distributions suggest that the subgenus Seriphidium is polyphyletic and that the section Tridentatae originated from Abrotanum. Consequently, the Tridentate should be recognized as a subgenus separate and distinct from the Old World Seriphidium. There was insufficient information from the subgenus Dracunculus for interpretation. 相似文献
128.
Prof. Dr. Dr. Karl-Heinz Wrobel Fred Sinowatz Roswitha Mademann 《Cell and tissue research》1981,217(2):289-310
Summary The intertubular stroma of the bovine testis is composed of narrow strands between two adjacent tubules and larger tri- and quadrangular interstices between three to four tubules. The latter contain the majority of Leydig cells, larger blood vessels and testicular lymph vessels. Ley dig cells occur in groups or cords, not every cell being in close contact to a capillary, lymph vessel or venule. Between adjacent Leydig cells intercellular canaliculi and gap junctions are frequently encountered. Bovine Leydig cells are further characterized by an abundance of ribosome-associated endoplasmic reticulum, by mitochondria often containing crystalloid structures and displaying both tubular and lamelliform cristae, as well as by a relative paucity of lipid droplets and lysosomes. Independent of the size of intertubular lymph vessels their walls consist only of an endothelium of varying thickness, no typical basal lamina or associated musculature being present. The interstitial surface of the endothelium sends anchoring cytoplasmic pedicles into the subjacent ground substance and collagen fibrils. Among occasional plasma cells, mast cells and mononuclear leucocytes, a regular constituent of the intertubular region studied is a population of electron-lucid, irregularly shaped cells (light intercalated cells = LIC) with slender, pleomorphic processes. These cells are believed to be involved in testicular androgen storage and distribution.Supported by a grant from the Deutsche Forschungsgemeinschaft 相似文献
129.
Summary In the present study the development of the bovine acrosome was investigated using conventional electron-microscopical techniques as well as the phosphotungstic-acid (PTA) technique (Rambourg 1967) including enzymatic digestion experiments. As in other species and in accordance with previous light-microscopical studies (Clermont and Leblond 1955) four phases of acrosomal differentiation can be discerned: the Golgi-phase, cap-phase, acrosome-phase, and maturation-phase.In the bull no internal pattern of the acrosomal content can be observed, either with conventional uranyl acetate-lead citrate staining or with the PTA-techniques. Our results support the observation in other species (Fawcett et al. 1971) that no intrinsic polymerization or crystallization process of the acrosomal content is responsible for acrosomal shaping. Some of our results suggest the influence of external forces on acrosomal development in the bull. During the cap-phase and the acrosome-phase accumulations of smooth endoplasmic reticulum and a layer of fine filaments can be observed in the Sertoli-cell cytoplasm, immediately adjacent to the developing acrosome. A temporary influence of these structures on acrosomal development seems possible. The PTA-positive staining of the developing bovine acrosome is probably due to the presence of acrosomal glycoproteins; however, our results do not exclude the possibility that molecules other than glycoproteins contribute to the positive PTA-staining of the developing acrosome.Supported by a grant from the Deutsche Forschungsgemeinschaft 相似文献
130.
Summary This report describes a female infant with a 47,X,del(X)(p11),+21 karyotype who has clinical features of both Down and Turner syndromes. The majority of her clinical features are suggestive of Down syndrome. 相似文献