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151.
Naruo Nikoh Naoyuki Iwabe Kei-ichi Kuma Mutsuhito Ohno Tsutomu Sugiyama Yoko Watanabe Kinya Yasui Zhang Shi-cui Katsuji Hori Yoshiro Shimura Takashi Miyata 《Journal of molecular evolution》1997,45(1):97-106
Previously we suggested that four proteins including aldolase and triose phosphate isomerase (TPI) evolved with approximately
constant rates over long periods covering the whole animal phyla. The constant rates of aldolase and TPI evolution were reexamined
based on three different models for estimating evolutionary distances. It was shown that the evolutionary rates remain essentially
unchanged in comparisons not only between different classes of vertebrates but also between vertebrates and arthropods and
even between animals and plants, irrespective of the models used. Thus these enzymes might be useful molecular clocks for
inferring divergence times of animal phyla. To know the divergence time of Parazoa and Eumetazoa and that of Cephalochordata
and Vertebrata, the aldolase cDNAs from Ephydatia fluviatilis, a freshwater sponge, and the TPI cDNAs from Ephydatia fluviatilis and Branchiostoma belcheri, an amphioxus, have been cloned and sequenced. Comparisons of the deduced amino acid sequences of aldolase and TPI from the
freshwater sponge with known sequences revealed that the Parazoa–Eumetazoa split occurred about 940 million years ago (Ma)
as determined by the average of two proteins and three models. Similarly, the aldolase and TPI clocks suggest that vertebrates
and amphioxus last shared a common ancestor around 700 Ma and they possibly diverged shortly after the divergence of deuterostomes
and protostomes. 相似文献
152.
Carol A. Sheppard Peter B. Simpson Alan H. Sharp Frederick C. Nucifora Christopher A. Ross †G. David Lange James T. Russell 《Journal of neurochemistry》1997,68(6):2317-2327
Abstract: We have examined the mechanisms that underlie Ca2+ wave propagation in cultured cortical astrocytes. Norepinephrine evoked Ca2+ waves in astrocytes that began at discrete initiation loci and propagated throughout the cell by regenerative amplification at a number of cellular sites, as shown by very high Ca2+ release rates at these regions. We have hypothesized previously that domains displaying elevated Ca2+ release kinetics in astrocytes may correspond to sites of high inositol 1,4,5-trisphosphate receptor (InsP3 R) density. To examine this possibility, we compared the distribution pattern of endoplasmic reticulum (ER) and InsP3 Rs with Ca2+ release kinetics in subcellular regions during propagation of norepinephrine-evoked waves. 3,3'-Dihexyloxacarbocyanine iodide staining revealed that the ER in astrocytes exists as a meshwork of membranes extending throughout the cells, including fine processes. A specific antibody directed against type 2 InsP3 Rs (InsP3 R2) detected a 260-kDa band in western blotting of astrocyte membranes. Immunocytochemistry using this antibody stained the entire ER system in a punctate, variegated manner. When Ca2+ responses and InsP3 R2 immunofluorescence were compared in the same cell, domains of elevated Ca2+ response kinetics (high amplitude and rapid rate of rise) showed significant positive correlation with high local intensity of InsP3 R2 staining. It appears, therefore, that specializations in the ER responsible for discrete local Ca2+ release sites that support regenerative wave propagation include increased levels of InsP3 R2 expression. 相似文献
153.
154.
Carbamoyl phosphate synthetase I (ammonia; E C 6.3.4.16) was purified from the liver of Rana catesbeiana (bullfrog). Crystals of the protein have been obtained at 22°C by the hanging drop vapor diffusion technique, with polyethylene glycol as precipitant. Tetragonal crystals of about 0.3 × 0.3 × 0.7 mm diffract at room temperature to at least 3.5 Å using a conventional source and are stable to X-radiation for about 12 h. Therefore, these crystals are suitablefor high resolution studies. The space group is P41212 (or its enantiomorph P43212), with unit cell dimensions a = b = 291.6 Å and c = 189.4 Å. Density packing considerations areconsistent with the presence of 4-6 monomers (Mr of the monomer, 160,000) in the asymmetric unit. Amino-terminal sequence of the enzyme and of a chymotryptic fragment of 73.7 kDa containing the COOH-terminus has been obtained. The extensive sequence identity with rat and human carbamoyl phosphate synthetase I indicates the relevance for mammals of structural data obtained with the frog enzyme. © 1995 Wiley-Liss, Inc. 相似文献
155.
A index for monitoring the trophic status of rivers based on diatom composition (‚trophic diatom index’, TDI) has been developed,
in response to the National Rivers Authority (England & Wales)'s needs under the terms of the Urban Wastewater Treatment Directive
of the European Community. The index is based on a suite of 86 taxa selected both for their indicator value and ease of identification.
When tested on a dataset from 70 sites free of significant organic pollution, this index was more highly correlated with aqueous
P concentrations than previous diatom indices. However, where there was heavy organic pollution, it was difficult to separate
the effects of eutrophication from other effects. For this reason, the value of TDI is supplemented by an indication of the
proportion of the sample that is composed of taxa tolerant to organic pollution.
The index was tested on the R. Browney, N-E. England, above and below a major sewage discharge. TDI values indicated that
the effect of inorganic nutrients on the river downstream of the discharge was slight as the river was already nutrient-rich,
but there was a large increase in the proportion of organic pollution-tolerant taxa. This indicates that the river was already
so eutrophic upstream of the discharge that tertiary treatment to remove P would not be effective unless other aspects of
the discharge were also improved. 相似文献
156.
George Lymberopoulos John N. Hawthorne 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》1984,805(3):285-290
Pig platelet phosphoinositides have been labelled with [3H]inositol and then treated with thrombin in the absence of Ca2+. There was a loss of labelled phosphatidylinositol 4,5-bisphosphate between 30 and 60 s after the addition of thrombin but the general picture was of increased labelling over a 4-min period. Labelling of phosphatidylinositol 4-phosphate showed no period of loss but there was an early loss of phosphatidylinositol and no increased labelling during the 4-min incubation. The small amount of lysophosphatidyl[3H]inositol in the platelets was not affected by thrombin treatment. Thrombin caused loss of [14C]arachidonate-labelled phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol. 相似文献
157.
The ratio of Photosystem (PS) II to PS I electron-transport capacity in spinach chloroplasts was compared from reaction-center and steady-state rate measurements. The reaction-center electron-transport capacity was based upon both the relative concentrations of the PS IIα, PS IIβ and PS I centers, and the number of chlorophyll molecules associated with each type of center. The reaction-center ratio of total PS II to PS I electron-transport capacity was about 1.8:1. Steady-state electron-transport capacity data were obtained from the rate of light-induced absorbance-change measurements in the presence of ferredoxin-NADP+, potassium ferricyanide and 2,5-dimethylbenzoquinone (DMQ). A new method was developed for determining the partition of reduced DMQ between the thylakoid membrane and the surrounding aqueous phase. The ratio of membrane-bound to aqueous DMQH2 was experimentally determined to be 1.3:1. When used at low concentrations (200 μM), potassium ferricyanide is shown to be strictly a PS I electron acceptor. At concentrations higher than 200 μM, ferricyanide intercepted electrons from the reducing side of PS II as well. The experimental rates of electron flow through PS II and PS I defined a PS II/PS I electron-transport capacity ratio of 1.6:1. 相似文献
158.
A 250-kilodalton cellular protein is induced by progestins in two human breast cancer cell lines MCF7 and T47D 总被引:1,自引:0,他引:1
We have studied the effect of R5020, a synthetic progestin, on the biosynthesis of cellular proteins extracted from the MCF7 and T47D human breast cancer cells, using gel electrophoresis. R5020 stimulates the synthesis, as measured after [35S]-methionine labelling, and the accumulation, as shown by silver staining, of a protein of molecular weight approximately equal to 250,000. The increase of the labelled 250-kilodalton protein was rapid (3 hours) and after 3 days this protein represented approximately equal to 6% of the total cellular proteins (approximately equal to 1 microgram/150,000 cells). The induction of the 250-kilodalton protein was obtained by physiologically active concentrations of several progestins and high concentrations of 5 alpha-dihydrotestosterone but not by estradiol or dexamethasone. It was inhibited by R486 , a progestin antagonist, but not by flutamide, an androgen antagonist. These results indicate a mediation by the progesterone receptor. The 250-kilodalton protein appears to be an excellent probe to study in cell culture the mechanism of action of progestin on human cells. 相似文献
159.
Rabbit heart mitochondria were used as a source of enzymes for the synthesis of phosphoruslabeled creatine phosphate. This method is based on the coupled reaction between mitochondrial oxidative phosphorylation and mitochondrial-bound creatine kinase. It is possible to convert more than 90% of the inorganic phosphate (Pi) to creatine phosphate. The method used only small amounts of adenine nucleotides which led to a product with only slight nucleotide contamination. This could be removed by activated charcoal extraction. For further purification, a method for the removal of residual Pi is described. 相似文献
160.
Changes in key regulatory enzymes of hepatic carbohydrate metabolism after glucose loading of starved rats 总被引:5,自引:0,他引:5
T H Claus F Nyfeler H A Muenkel M G Burns T Pate S J Pilkis 《Biochemical and biophysical research communications》1984,125(2):655-661
When glucose was given to starved rats there was an increase in both 6-phosphofructo 2-kinase and pyruvate kinase activity and a decrease in fructose 2,6-bisphosphatase activity 30 min and 60 min later. These changes were accompanied by an increase in glycogen deposition and by modest, but significant increases in fructose 2,6-bisphosphate levels at the same time. Metabolite measurements indicated that flux through 6-phosphofructo 1-kinase and pyruvate kinase were increased. These results suggest that although glycogen deposition may occur via the gluconeogenic pathway, glycolysis is activated at the same time by changes in the phosphorylation state of key regulatory enzymes as well as by the small rise in fructose 2,6-bisphosphate. 相似文献