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31.
The effect of charge of the Fe(II) reagent used to induce DNA strand cleavage reactions in the presence of a source of reducing equivalents is investigated using two oligonucleotide models. The first consists of the two strands dA20 and dT20, and an equimolar complex between them. The second is a short four-arm branched DNA complex composed of four 16-mer strands. In the former case, cleavage of the 1:1 complex by three reagents with different formal charge, Fe(II).EDTA2-, Fe(II).EDDA and Fe2+, is comparable in rate to that of the individual dT20 and the dA20 strands. While the three reagents show similar cleavage rates for the duplex and single stranded molecules, they give distinctive cutting patterns in the DNA tetramer, consistent with the presence of a site of excess negative charge at the branch point. Scission induced by Fe(II).EDTA2- shows lower reactivity at the branch site relative to duplex controls, whereas Fe(II)2+ shows enhanced reactivity. Formally neutral Fe(II).EDDA shows weak loss of cutting reactivity at the branch. The position of attack by Fe(II)2+ in the branched tetramer is shifted with respect to those of Fe(II).EDTA2- or Fe(II).EDDA; a slower migrating species is also detected in the scission of dA20.dT20 duplex by Fe(II) reaction. These results suggest that the Fe(II)2+ reaction proceeds by a different mechanism from the other agents. The difference in cutting profiles induced by the neutral and negatively charged chelated complexes is consistent with a local electrostatic repulsion of a negatively charged source of radicals, not a positively charged one. 相似文献
32.
Metabolism of phospholipids on erythrocyte membranes 总被引:2,自引:0,他引:2
33.
N R Kallenbach M Lu N Vasant Kumar J W Nelson 《Journal of biomolecular structure & dynamics》1990,7(4):973-983
The effect of the distribution of charged residues on stability of alpha helices in isolated peptides and in globular proteins exemplified by myoglobins from 62 different species is discussed. A highly simplified set of rules is used to account for the interaction of charged groups with the dipole of an alpha helix. Only the position and sign of a charge with respect to the center of the helix and its ability to participate in intrahelical salt bridges determine its effect. These rules lead to a linear correlation between the helicity in variant C-peptide helices from RNAse and the extent to which the charge distribution opposes the helix dipole. Of the sample of 496 helices in the myoglobins studied, 456 exhibit arrangements of charges which oppose the effective dipole moment of the helix according to this calculation. A number of variants occur which leave the backbone moment of helices A-D unchanged, or even add to it. However no such variants exist in the sequences of helices E-H. We suggest that the E, F, G and H helices in myoglobins which show the strongest reversal of the helix dipole participate in the structures of early intermediates in folding of the chain. Stable helix structures should be more likely to occur in these isolated sequences also, and introduction of charge alterations in helices E to H should affect the initial refolding rate of mutant myoglobins. 相似文献
34.
The periplasmic location of enzymes A and B of the thiosulphate-oxidizing multienzyme system of Thiobacillus versutus has been further confirmed by differential radiolabelling of periplasmic and cytoplasmic proteins. The stoichiometries of respiration-driven proton translocation in T. versutus were determined using the oxygen pulse and the initial rate methods. A value for the H+/O quotient (number of protons translocated per oxygen atom reduced) of about 2.8 was found for the oxidation of thiosulphate, and of about 2.5 for sulphite. The H+/O quotient for endogenous respiration was about 5.7. The data are shown to be in good agreement with the scheme proposed previously for thiosulphate oxidation by this organism. Proton generation during the oxidation of thiosulphate or sulphite is indicated to occur in the periplasm rather than by pumping across the cytoplasmic membrane. The results also suggest that a H+/O quotient of six occurs during NADH oxidation (from endogenous metabolism measurements) and that the terminal cytochrome oxidase, aa3, does not function as a proton pump.Abbreviations DCCD
dicyclohexyl carbodiimide
- FCCP
carbonyl cyanide p-trifluoromethoxyphenylhydrazone
- HQNO
2-n-heptyl-4-hydroxyquinoline N-oxide
- TMPD
N,N,N,N-tetramethyl-p-phenylenediamine
- IEF
isoelectric focusing
- HIC
hydrophobic interaction chromatography
- EAI
ethyl acetimidate hydrochloride
- IAI
isethionyl acetimidate 相似文献
35.
K Yamakawa S Kamiya S Nishida K Yoshimura H Yu D Y Lu S Nakamura 《Microbiology and immunology》1988,32(6):579-587
Soil specimens obtained from several areas of Japan, which are closely located to or facing the Continental land of China, were examined for the distribution of Clostridium botulinum, especially pertaining to types A and B. A total of 266 specimens of Japan, when cultured, showed no type A or B toxicity, although 30 (11.3%), 4 (1.5%), and 10 (3.8%) of the specimens showed C1, C2, and type E toxicities, respectively. On the contrary, types A and/or B toxicities were shown, by the same method, in 14 of 20 specimens of Shinkiang district, China. The highest number of C. botulinum cells found in one gram of soil specimen was 25 for type A and 10 for type B. 相似文献
36.
四川宝兴雉类生态和垂直分布的调查研究 总被引:2,自引:0,他引:2
宝兴位于四川盆地西缘山地,境内纵贯世界闻名的大雪山——即夹金山。 自19世纪30年代至20世纪30年代,先后有Verreaux(1838—1871),Geoffroy(1866),David(1871),Seinhoe(1871),Sharpe(1875),David et Oustalet(1877),Oustaler (1891—92),Styan(1899),Laubmann(1920),La Touch(1925—30),Smith(1931—34),Bangs(1932),Seys(1934)等对宝兴进行过调查和采集,而我 相似文献
37.
A small basic peptide with an unusual amino acid composition has been isolated from the seeds of pumpkin, Cucurbita maxima. Amino acid analysis and sequence data show the protein to be about 36 residues in length, with an approximate composition Lys1, Arg14, Asp3, (Glu + Gln)15, Gly1, Pro1, Trp1. On the basis of composition, the molecular weight is approximately 5000 daltons and the nitrogen content by weight is 20.4%. Twelve amino acids are entirely lacking. The peptide is slightly toxic to mouse B-16 melanoma cells, but its in vivo function is unknown. It does not appear to be derived from cucurbitin, the pumpkin storage globulin; however, it could be a storage peptide involved in nitrogen mobilization during the early stages of germination. 相似文献
38.
Summary Callus cultures ofPicea engelmannii (Parry, Engelmann spruce) were initiated and established from mature embryos cultured on von Arnold and Eriksson’s medium
(AE) supplemented with N6-benzyladenine (10μM) and naphthalene acetic acid (10 μM). Cultures were maintained by subculture at 3-to-4-wk intervals. After three subcultures, callus was transferred to AE medium
with only N6-benzyladenine (25 μM). Adventitious buds appeared on the surface of the callus after 2-to 4-wk and grew to adventitious shoots on AE medium without
growth hormones or on AE medium with kinetin (0.1 μM). Shoot-forming capacity was maintained through 7 further subcultures.
This study was supported by the Natural Sciences and Engineering Research Council of Canada grant G1438 to T. A. Thorpe and
D. I. Dunstan. 相似文献
39.
Protein synthesis in the hippocampus associated with memory facilitation by corticotropin-releasing factor in rats. 总被引:2,自引:0,他引:2
The present study used pharmacological, biochemical, and behavioral methods to examine the role of protein synthesis in the hippocampus in memory processes of a passive avoidance learning in rats. Results indicated that corticotropin-releasing factor (CRF) significantly improved memory retention in rats. Both cycloheximide (CHX) and actinomycin-D (ACT-D) impaired memory at high doses. At doses of CHX and ACT-D that did not affect memory alone, they both antagonized the memory-enhancing effect of CRF. Biochemically, there were specific increases in the optical density of three protein bands in the cytosolic fraction of hippocampal cells in rats showing good memory. There were also marked increases in the optical density of two protein bands in the nucleus fraction of the same animals. Similar results were observed in animals injected with CRF. However, no significant protein alteration was observed in animals receiving stress. These results together suggest that there are new protein syntheses in the hippocampus that are specifically associated with passive avoidance learning in rats. 相似文献
40.
热应激时大鼠肺组织中β—肾上腺素受体的变化与膜磷... 总被引:4,自引:1,他引:3
To explore the relationship between the change of beta-adrenoceptor and the metabolism of phospholipids in lung tissue from acute heat stressed rats, the Bmax of beta-adrenoceptors, the activity of phospholipase A2 (PLA2), the content of phosphatidylcholine (PC) and phosphatidylserine (PS), and membrane fluidity in lung tissue of normal and heat stressed rats were investigated. The relevant parameter values mentioned above were 479 +/- 94 fmol/mg protein, 78.5 +/- 8.2 U, 53.5 +/- 1.7 mg/g.wet. w. and 425.1 +/- 68.1 micrograms/g.wet. w. respectively. Whereas in the heat stressed rats with rectal temperature raised to 42 degrees C for 15 min, the Bmax of beta-adrenoceptor was decreased by 43% (P less than 0.01), the activity of PLA2 increased by 83% (P less than 0.01), the contents of PC and PS decreased by 50% and 47% (P less than 0.01) respectively. A lower membrane fluidity in lung tissue for heat stressed rats was also demonstrated. The results suggest that the decreased binding sites of beta-adrenoceptor in lung tissue of rat during hyperthermia may be contributed to the activation of PLA2, which then accelerated the catabolism of phospholipids such as PC and PS in the cell plasma membrane, with a consequent alteration of membrane fluidity. 相似文献