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31.
A method is proposed for predicting the adjacency order in which strands pack in a -sheet in a protein, on the basis of its amino acid sequence alone. The method is based on the construction of a predicted contact map for the protein, in which the probability that various residue pairs are close to each other is computed from statistically determined average distances of residue pairs in globular proteins of known structure. Compact regions, i.e., portions of the sequence with many interresidue contacts, are determined on the map by using an objective search procedure. The proximity of strands in a -sheet is predicted from the density of contacts in compact regions associated with each pair of strands. The most probable -sheet structures are those with the highest density of contacts. The method has been tested by computing the probable strand arrangements in a five-strand -sheet in five proteins or protein domains, containing 62–138 residues. Of the theoretically possible 60 strand arrangements, the method selects two to eight arrangements as most probable; i.e., it leads to a large reduction in the number of possibilities. The native strand arrangement is among those predicted for three of the five proteins. For the other two, it would be included in the prediction by a slight relaxation of the cutoff criteria used to analyze the density of contacts. 相似文献
32.
Adam Slivka Mary Beth Spina Harold I. Calvin Gerald Cohen 《Journal of neurochemistry》1988,50(5):1391-1393
Previous studies indicated that DL-buthionine sulfoximine (DL-BSO), an agent that inhibits the biosynthesis of GSH in liver and other peripheral organs, fails to suppress levels of GSH in the CNS. In the current study, preweanling mice responded to repeated injections of L-BSO with marked declines (79.6-86.5%) of GSH content in brain and spinal cord. In adult mice, the same treatment schedule produced only modest declines (17.8-29.2%) of GSH content in brain and a 55.9% decline in spinal cord. Pretreatment of preweanling mice with L-BSO represents a tool for studying the role of GSH in the CNS. 相似文献
33.
Glycine decarboxylase is confined to the bundle-sheath cells of leaves of C3−C4 intermediate species
Christopher M. Hylton Stephen Rawsthorne Alison M. Smith D. Alan Jones Harold W. Woolhouse 《Planta》1988,175(4):452-459
Immunogold labelling has been used to determine the cellular distribution of glycine decarboxylase in leaves of C3, C3–C4 intermediate and C4 species in the genera Moricandia, Panicum, Flaveria and Mollugo. In the C3 species Moricandia foleyi and Panicum laxum, glycine decarboxylase was present in the mitochondria of both mesophyll and bundle-sheath cells. However, in all the C3–C4 intermediate (M. arvensis var. garamatum, M. nitens, M. sinaica, M. spinosa, M. suffruticosa, P. milioides, Flaveria floridana, F. linearis, Mollugo verticillata) and C4 (P. prionitis, F. trinervia) species studied glycine decarboxylase was present in the mitochondria of only the bundle-sheath cells. The bundle-sheath cells of all the C3–C4 intermediate species have on their centripetal faces numerous mitochondria which are larger in profile area than those in mesophyll cells and are in close association with chloroplasts and peroxisomes. Confinement of glycine decarboxylase to the bundle-sheath cells is likely to improve the potential for recapture of photorespired CO2 via the Calvin cycle and could account for the low rate of photorespiration in all C3–C4 intermediate species.Abbreviation and symbol kDa
kilodaltons
-
CO2 compensation point 相似文献
34.
35.
ATP-dependent bacterial transporters and cystic fibrosis: analogy between channels and transporters.
The traffic ATPases superfamily includes known transporters, both prokaryotic and eukaryotic, including the medically important proteins, P-glycoprotein, and the cystic fibrosis gene product (CFTR), which is known to be a Cl- channel. The structure and mechanism of action of the best-studied members of the superfamily, the periplasmic permeases, are described and related to that of CFTR and eukaryotic traffic ATPases in general. The contention is put forward that the distinction between the architecture and mechanisms of action of channels and transporters is blurred. 相似文献
36.
Concentrations of manganese were determined in the liver, kidney, muscle and bone of white suckers (Catostomus commersoni) from five acid (pH < 5.8), and two circumneutral lakes in south-central Ontario. Manganese tissue concentrations were greater in fish captured from the most acidified lakes with the greatest concentrations of dissolved manganese. These fish had increased concentrations of manganese in the liver, as indicated by a comparison of liver:kidney manganese concentration ratios among the seven fish populations. Tissue concentrations of manganese from all populations either were negatively correlated (P < 0.05) or remained constant with fish size indicating homeostatic regulation of this metal. Manganese concentrations of the benthic fauna were positively correlated to sediment concentrations (R=0.30). Lake sediment manganese concentrations were significantly correlated to maximum lake depth (R=0.80, P < 0.03), with the concentrations in the top 0–1 cm dependent on the redox conditions in the seven lakes. Based on the seven lakes studied, manganese concentrations in the benthic-feeding white sucker correlated better with dissolved manganese, than with either the concentrations in food or surficial sediments. 相似文献
37.
Cloning, Expression, and Purification of Glutamine Synthetase from Clostridium acetobutylicum 总被引:7,自引:1,他引:6
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A glutamine synthetase (GS) gene, glnA, from the gram-positive obligate anaerobe Clostridium acetobutylicum was cloned on recombinant plasmid pHZ200 and enabled Escherichia coli glnA deletion mutants to utilize (NH4)2SO4 as a sole source of nitrogen. The cloned C. acetobutylicum gene was expressed from a regulatory region contained within the cloned DNA fragment. glnA expression was subject to nitrogen regulation in E. coli. This cloned glnA DNA did not enable an E. coli glnA ntrB ntrC deletion mutant to utilize arginine or low levels of glutamine as sole nitrogen sources, and failed to activate histidase activity in this strain which contained the Klebsiella aerogenes hut operon. The GS produced by pHZ200 was purified and had an apparent subunit molecular weight of approximately 59,000. There was no DNA or protein homology between the cloned C. acetobutylicum glnA gene and GS and the corresponding gene and GS from E. coli. The C. acetobutylicum GS was inhibited by Mg2+ in the γ-glutamyl transferase assay, but there was no evidence that the GS was adenylylated. 相似文献
38.
John H. Caldwell Jennifer Van Brunt Franklin M. Harold 《The Journal of membrane biology》1986,89(1):85-97
Summary Injection of depolarizing current into vegetative cells of the water moldBlastocladiella emersonii elicits a regenerative response that has the electrical characteristics of an action potential. Once they have been taken past a threshold of about –40 mV, cells abruptly depolarize to +20 mV or above; after an interval ranging from several hundred milliseconds to a few seconds, the cells spontaneously return to their resting potential near –100 mV. When the action potential was analyzed with voltage-clamp recording, it proved to be biphasic. The initial phase reflects an influx of calcium ions through voltage-sensitive channels that also carry Sr2+ ions. The delayed, and more extended, phase of inward current results from the efflux of chloride and other anions. The anion channels are broadly selective, passing chloride, nitrate, phosphate, acetate, succinate and even PIPES. The anion channels open in response to the entry of calcium ions, but do not recognize Sr2+. Calcium channels, anion channels and calcium-specific receptors that link the two channels appear to form an ensemble whose physiological function is not known. Action potentials rarely occur spontaneously but can be elicited by osmotic downshock, suggesting that the ion channels may be involved in the regulation of turgor. 相似文献
39.
Evolution of karyotypic abnormalities and C-MYC oncogene amplification in human colonic carcinoma cell lines 总被引:7,自引:0,他引:7
C. C. Lin Kari Alitalo Manfred Schwab Donna George Harold E. Varmus J. Michael Bishop 《Chromosoma》1985,92(1):11-15
Cell lines (COLO 320 DM and COLO 320 HSR), established from a human neuroendocrine tumor, contain an amplified cellular oncogene (c-myc). We have previously shown that the homogeneously staining regions (HSRs) of a marker chromosome in the COLO 320 HSR cells that evolved in culture from COLO 320 DM cells contain amplified c-myc. Molecular hybridization in situ has now been used to demonstrate that the HSRs are on both arms of what was once an X chromosome. We also show that amplified c-myc copies are present in the isolated double minute chromosomes (DMs) of the COLO 320 DM cells that were characteristic of the tumor cells initially established from the patient. The results suggest that the amplified c-myc appeared first as DMs and was subsequently transposed to engender HSRs on an X chromosome. The initial COLO 320 tumor cell may have acquired two early replicating (i.e., active) X chromosomes and lost the late replicating (i.e., inactive) X. 相似文献
40.
Summary The homeothermic capacity of chicks varied as a function of brood size, age, and air temperature. Commitment to brooding by parents also varied as a function of brood size, age of the young brooded, and prevailing air temperature. It was experimentally determined that parents altered their brooding commitment in direct response to the achieved mean homeothermic capacity of the brood rather than energy demands of the brood per se. Because larger broods achieved a given level of homeothermic capacity earlier than smaller broods, parents spent less time brooding larger broods. This freed time represented an increase in potential foraging time by the parents. However, there was no evidence that parents used this potential increased foraging time to elevate the energy return to the nestlings. Other possible advantages of a facultative brooding response by parents are discussed. 相似文献