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941.
The molecular weight of Artemia ribosomes, as determined from their refractive-index increment and light-scattering intensity 下载免费PDF全文
Cytoplasmic ribosomes were isolated from the cryptobiotic embryos of the brine shrimp Artemia salina. Measurements of their refractive-index increments and light-scattering intensities give a value for their molecular weight of (3.4±0.2)×106. 相似文献
942.
Summary
Typosyllis pulchra reproduces by the production of three to four gamete-bearing stolons (schizogamy) during consecutive 30-day periods. Although gonads are found in a large number of segments, only those in the posterior-most segments produce gametes and become incorporated into the developing stolon. The more anterior gonads remain undifferentiated and probably sexually undetermined until they are needed in future stolonizations. Gonial cells, which will eventually become either male or female, are ultrastructurally identical at the onset of each stolonization period. Spermatogenesis is marked by a short proliferative period followed by differentiation and spermiogenesis. The first ultrastructural signs of spermatogenesis were found in coelomic spermatogonia on day 10 of stolon formation. Spermatogonia are joined by intercellular bridges, which are maintained until the early spermatid stage. Synaptonemal complexes mark the onset of meiosis, which is apparently synchronized in the syncytial clusters of primary spermatocytes. Spermiogenesis occurs during the final 10 days of stolonization and a variety of stages is present within a single animal. All sperm mature by the time the stolon detaches. Acrosome formation and nuclear condensation are described in addition to the ultrastructure of mature sperm. 相似文献
943.
A Bacillus sp., isolated by anaerobic enrichment on a o-phthalic acid-nitrate medium, grew either aerobically or anaerobically on phthalic acid. Cells grown anaerobically on phthalate immediately oxidized phthalate and benzoate with nitrate, whereas aerobic oxidation only occurred after a lag period and was inhibited by chloramphenicol. 2-Fluoro-and 3-fluorobenzoate were formed from 3-fluorophthalate by cells grown anaerobically on phthalate. Aerobically grown cells immediately oxidized phthalate, benzoate, 3-hydroxybenzoate and gentisate with oxygen. The aerobic and anaerobic route of catabolism of phthalate may thus share an initial decarboxylation to benzoate. This is the first report of the anaerobic dissimilation of phthalic acid by a pure bacterial culture. 相似文献
944.
Hydrogen-oxidizing acetogenic bacteria in pure culture are presently represented by the two mesophilic species, Acetobacterium woodii and Clostridium aceticum. From Lake Kivu we have isolated a Gram negative, chemolithotrophic, thermophilic anaerobe (LKT-1) that oxidizes hydrogen and reduces carbon dioxide to acetic acid. It is a non-motile, non-sporeforming rod, about 0.7m in width and 2–7.5m in length, often occuring in pairs or chains. The cell wall has a banded appearance; the surface layer contains a regular array of particles with six-fold rotational symmetry. No outer membrane is present. The temperature optimum for growth is 66°C, and the pH optimum is 6.4. Organic growth substrates include glucose, mannose, fructose, pyruvate, and formate; acetate is the principal product. The doubling time for growth on hydrogen and carbon dioxide is about 2h. Vitamins are neither required nor stimulatory. Yeast extract and Trypticase enhance the final yield but do not affect the growth rate. Cysteine or sulfide are required and cannot be replaced by thioglycolate or dithiothreitol. LKT-1 was mass cultured on hydrogen and carbon dioxide in a 24.1 fermentor with a yield of 34g (wet weight) of cells. The DNA base composition as determined by buoyant density is 38 mol % guanine plus cytosine. LKT-1 appears only distantly related to physiologically similar bacteria. A new genus Acetogenium is proposed, and the species is Acetogenium kivui. 相似文献
945.
The ultrastructure of developing and mature nonarticulated laticifers in Asclepias syriaca L. (the common milkweed) was studied by conventional fixation and staining techniques and by osmium impregnation techniques. The mature laticifer protoplast in A. syriaca possesses a large central vacuole with an intact vacuolar membrane. Formation of this vacuole apparently results from dilation and subsequent enlargement of endoplasmic reticulum and possibly in part by fusion of smaller vacuoles and limited cellular-lytic autophagy. Widespread digestion or autophagy of cytoplasm within vacuoles is not evident. Nuclei, mitochondria, dictyosomes, and small vesicles are the most prominent components distributed in the peripheral cytoplasm. Plastids appear to degenerate as the laticifer matures. The specialized cellular component, latex, which is the vacuolar content of the laticifer, is interpreted to be produced in the cytoplasm and subsequently incorporated into the large central vacuole. Rubber globules, the most prominent latex component, are surrounded by a membrane that does not have a trilaminate structure. Globules are associated with an electron-dense fibrillar component in the vacuole. 相似文献
946.
Changes in the kinetic behaviour of threonine transport into Trypanosoma brucei elicited by variation in hydrogen ion concentration 下载免费PDF全文
H. Paul Voorheis 《The Biochemical journal》1977,164(1):15-25
1. The dependence of V and V/K(m) for threonine transport into Trypanosoma brucei upon the external concentration of H(+) was studied. 2. Two ionizing groups, the alpha-amino group of the substrate and a group at the substrate-binding site of the carrier, were found to influence the observed kinetic behaviour of transport. 3. The pK of the group at the substrate-binding site on the free carrier was found to be 6.95 at 30 degrees C and to be temperature-dependent; its heat of ionization was -63.8kJ, which is outside the range for most proton dissociations and suggests a significant contribution from some other source, possibly the remainder of the carrier or the membrane environment. 4. Binding of substrate caused the pK of its alpha-amino group to shift to a higher value, whereas that of the carrier group shifted to a lower value (6.65 at 30 degrees C). 5. The ionic interaction between substrate and carrier appeared to be involved in the stabilizing of the protonated substrate and the species of the carrier-substrate complex required for the membrane-translocation step. 6. The same ionic species of carrier-substrate complex is required for both substrate dissociation and translocation of the substrate through the membrane. 7. H(+) symport or antiport did not occur during threonine uptake. 相似文献
947.
Norio Ogawa Tom Thompson Henry G. Friesen Joseph B. Martin Paul Brazeau 《The Biochemical journal》1977,165(2):269-277
A soluble somatostatin-binding protein was detected in the cytosol fractions of various rat, human and bovine tissues. Maximum binding occurred at pH8.0-8.5 and was Ca(2+)-dependent. The specific binding of somatostatin per 10mug of cytosol protein from 12 rat tissues ranged between 36 and 15%, and 3% for peripheral blood cells. There was also substantial binding in cytosol from human anterior pituitary and liver, and bovine anterior pituitary. The specific binding in rat and human plasma in the presence of EDTA was only 1%. Gel filtration suggested a molecular weight of approx. 80000 for the somatostatin-binding protein from several sources. Exposure of the binding protein to trypsin eliminates somatostatin-binding activity but ribonuclease and deoxyribonuclease have no effect. The binding protein is thermolabile, ethanol-precipitable, and not completely specific for somatostatin. Bound (125)I-labelled [Tyr(1)]somatostatin is not easily displaced by excess of unlabelled somatostatin. The effects of dithiothreitol and mercaptoethanol on the binding of (125)I-labelled [Tyr(1)]somatostatin to the binding protein suggests that binding involves two sequential steps, first loose binding, then disulphide linkage. Since semipurified somatostatin-binding protein causes a dose-related inhibition of the binding of (125)I-labelled [Tyr(1)]somatostatin in radioimmunoassays for somatostatin, estimates of somatostatin content of tissue extracts by radioimmunoassay in some cases may be spuriously high. It is not yet clear whether the binding protein is a true cytosol protein or an easily solubilized membrane protein. 相似文献
948.
1. Fatty acid synthesis was studied in microsomal preparations from germinating pea (Pisum sativum). 2. The preparations synthesized a mixture of saturated fatty acids up to a chain length of C(24) from [(14)C]malonyl-CoA. 3. Whereas hexadecanoic acid was made de novo, octadecanoic acid and icosanoic acid were synthesized by elongation. 4. The products formed during [(14)C]malonyl-CoA incubation were analysed, and unesterified fatty acids and polar lipids were found to be major products. [(14)C]Palmitic acid represented a high percentage of the acyl-carrier protein esters, whereas (14)C-labelled very-long-chain fatty acids were mainly present as unesterified fatty acids. CoA esters were minor products. 5. The addition of exogenous lipids to the incubation system usually resulted in stimulation of [(14)C]malonyl-CoA incorporation into fatty acids. The greatest stimulation was obtained with dipalmitoyl phosphatidylcholine. Both exogenous palmitic acid and dipalmitoyl phosphatidylcholine increased the amount of [(14)C]-stearic acid synthesized, relative to [(14)C]palmitic acid. Addition of stearic acid increased the amount of [(14)C]icosanoic acid formed. 6. [(14)C]Stearic acid was elongated more effectively to icosanoic acid than [(14)C]stearoyl-CoA, and its conversion was not decreased by addition of unlabelled stearoyl-CoA. 7. Incorporation of [(14)C]malonyl-CoA into fatty acids was markedly decreased by iodoacetamide and 5,5'-dithiobis-(2-nitrobenzoic acid). Palmitate elongation was sensitive to arsenite addition, and stearate elongation to the presence of Triton X-100 or fluoride. The action of fluoride was not, apparently, due to chelation. 8. The microsomal preparations differed from soluble fractions from germinating pea in (a) synthesizing very-long-chain fatty acids, (b) not utilizing exogenous palmitate-acyl-carrier protein as a substrate for palmitate elongation and (c) having fatty acid synthesis stimulated by the addition of certain complex lipids. 相似文献
949.
The association of the sulphogalactosylglycerolipid of rat brain with myelination 总被引:2,自引:1,他引:1 下载免费PDF全文
Joanne Pieringer G. Subba Rao Paul Mandel Ronald A. Pieringer 《The Biochemical journal》1977,166(3):421-428
The sulphogalactosylglycerolipid of rat brain is closely associated with the process of myelination, as demonstrated by the following observations. 1. The lipid is barely detectable in rat brain before 10 days of age, accumulates rapidly between age 10 and 25 days, and remains relatively constant in amount (between 0.3 and 0.4mumol per brain) thereafter into adult life. 2. The activity of adenosine 3'-phosphate 5'-sulphatophosphate-galactosyldiacylglycerol sulphotransferase is almost absent before 10 days of age, attains a maximum at age 20 days, and slowly decreases thereafter with increasing age. This developmental pattern correlates well with that of other myelin-specific metabolites. 3. Both the concentration of the sulphogalactosylglycerolipid and the activity of sulphotransferase are greatly decreased in the non-myelinating jimpy mouse. 4. The myelin fraction of rat brain contains most of the sulphogalactosylglycerolipid. The lipid occurs in a diacyl and an alkylacyl form. Determinations of the relative amount of each type in brain showed about a 1:1 mixture in both 21-day-old and adult rats. Rats injected with H(2) (35)SO(4) at 20 days of age lost (35)S from the diacyl form at a higher rate than from the alkylacyl compound over a 21-day period. These data suggest that the diacyl form has a higher turnover than the alkylacyl derivative. The percentage of the total sulpholipid content of brain contributed by the sulphogalactosylglycerolipid is 16% in 21-day-old rats and 8.4% in adult rats. 相似文献
950.
Summary The degenerative reaction of mitochondria to tricresylphosphate (TCP) poisoning in spinal ganglion cells of Slow Loris (Nycticebus coucang coucang) were studied with the electron microscope. In neurones of animals treated with TCP, mitochondria display various stages of alterations which confirm mitochondrial involvement in TCP poisoning. The role of degenerated mitochondria in the formation of neuronal lipofuscin is discussed. It is suggested that the lipofuscin granule is a metabolic product inherently related to mitochondrial degeneration, irrespective of the primary cause: ageing or intoxication.Fellow of the Deutscher Akademischer Austauschdienst on study leave from the Medical Faculty, University of SingaporeA grant from the Deutsche Forschungsgemeinschaft (Gl. 28/20) is gratefully acknowledgedThe skilfull technical assistance of Mr. Tajuddin b.M. Ali, Mr. P. Gopal, Mr. R. Dungan and Mrs. C. Weinrichter is gratefully acknowledged 相似文献