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941.
Jila H. Boal Scott F. Deamond Daniel E. Callahan Sarah A. Bruce Paul O. P. Ts'o L. L. Kan 《Cell biochemistry and biophysics》1989,14(3):245-256
The nuclear magnetic resonance (NMR) parameters, spin-lattice (T1), and spin-spin (T2) relaxation time, are usually longer for neoplastic cells than for normal cells of the same cell type. This has generally
been true at low NMR frequencies (≤100 MHz) when comparisons have been made between normal and neoplastic cells that have
both spent a short time in culture. We have previously demonstrated that although the T1 values of paired normal and neoplastic Syrian hamster (SH) fibroblastic cells in culture are not significantly different
when measured at 300 MHz, the 300 MHz T2 values for the neoplastic cells are smaller than those of the normal cells. (Xin et al. (1986),Cell Biophysics
8, 213.) Since treatment of normal diploid cells with polypeptide growth factors or tumor promoters frequently results in reversible
expression of neoplasia-associated phenotypes, T1 and T2 were obtained at 300 MHz for treated and untreated SH cells to see if these compounds could also produce smaller 300 MHz
T2 values. Secondary culture SH fetal fibroblast cells were treated with epidermal growth factor (EGF), fibroblast growth factor
(FGF), phorbol-12,13-didecanoate (PDD) and 4-α-phorbol-12,13-didecanoate (4αPDD). Treatment with either growth factor resulted
in smaller T2 values, but a statistically significant decrease was not observed for PDD or 4αPDD. The observed reductions in T2 values were correlated with the morphological and growth-stimulatory effects of these compounds on the cells. 相似文献
942.
Charles Illingworth Gregg Larson Goran Hellekant 《Journal of industrial microbiology & biotechnology》1989,4(1):37-42
Summary To produce and direct the export inStreptomyces lividans of the sweet plant protein thaumatin, thaumatin II cDNA was fused in the correct reading frame to the -galactosidase leader peptide, under the control of the -galactosidase promoter and ribosome binding site. The export of the recombinant thaumatin may allow the correct formation of the thaumatin disulfide bonds. The recombinant thaumatin was purified from the medium on an S-Sepharose column and detected with western blots by sheep -thaumatin antibodies. The recombinant thaumatin was the same size as authentic thaumatin and changed position on an acrylamide gel in response to reduction by 2-mercaptoethanol in the same manner. 相似文献
943.
溶液培养小麦幼苗转移至含Cd~(2 )的营养液中,根系乙烯产生较快地增加,约在12h达高峰,然后下降;ACC含量亦呈先升后降的趋势。未和Cd~(2 )溶液直接接触的地上部乙烯亦增加,至36h达高峰,此后急剧下降,而ACG和 MAGC含量持续上升。地上部乙烯的增加,主要是由通过根系运往地上部的镉直接作用的结果,不是根部合成ACG运往地上部后再产生的。电镜观察表明,地上部乙烯产生和ACC含量变化的时间进程,可以与镉进入叶细胞内的部位及其对细胞膜和细胞器的影响相联系。 相似文献
944.
945.
Charles F. Aylsworth James E. Trosko Chia C. Chang K. Benjamin Elizabeth Lockwood 《Cell biology and toxicology》1989,5(1):27-37
The effects of TPA and/or DDT and oleic acid and/or DDT on gap junction-mediated intercellular communication (i.e. metabolic cooperation) between Chinese hamster V79 cells was examined. Addition of TPA, DDT or oleic acid alone to cocultures of 6t-hioguanine-resistant (6-TG
R
) and 6-thioguanine-sensitive (6-TG
S
) V79 cells significantly increased the recovery of 6-TG
R
cells indicating inhibition of metabolic cooperation. In the presence of TPA and DDT or oleic acid and DDT the observed recovery of 6-TG
R
cells was significantly greater than the expected (calculated) additive 6-TG
R
cell recovery. No synergistic increases in 6-TG
R
cell recovery were observed when co-cultures of V79 cells were exposed to dieldrin and DDT. These results indicate that TPA and DDT or oleic acid and DDT can act synergistically to inhibit metabolic cooperation. These data suggest a role for protein kinase C in the regulation of gap junction-mediated intercellular communication.Abbreviations DDT
dichlorodiphenyltrichlorethane
- MC
metabolic cooperation defective
- 6-TG
6thioguanine
- TPA
12-0-tetradecanoylphorbol-13-acetate 相似文献
946.
Vanadate-stimulated oxidation of NAD(P)H 总被引:1,自引:0,他引:1
Vanadate stimulates the oxidation of NAD(P)H by biological membranes because such membranes contain NAD(P)H oxidases which are capable of reducing dioxygen to O2− and because vanadate catalyzes the oxidation of NAD(P)H by O2−, by a free radical chain mechanism. Dihydropyridines, such as reduced nicotinamide mononucleotide (NMNH), which are not substrates for membrane-associated NAD(P)H oxidases, are not oxidized by membranes plus vanadate unless NAD(P)H is present to serve as a source of O2−. When [NMNH] greatly exceeds [NAD(P)H], in such reaction mixtures, one can observe the oxidation of many molecules of NMNH per NAD(P)H consumed. This reflects the chain length of the free radical chain mechanism. We have discussed the mechanism and significance of this process and have tried to clarify the pertinent but confusing literature. 相似文献
947.
The authors examined relationships between Kira's warmth index (WI) and four other important thermal indices: the sums of
daily mean temperatures above 5°C and 10°C, Thornthwaite's potential evapotranspiration (PE) and Holdridge's annual biotemperature.
The thermal records of 671 meteorological stations evenly located all over China were used to make these comparisons. Close
correlations were found within the four relationships, and accordingly WI was used to analyse the thermal distributions of
the main vegetation types. Vegetation types around the 671 stations were read from a vegetation map with a scale of 1/4000000.
Vegetation types at 269 stations corresponded to the natural or seminatural vegetation, and 29 vegetation types were distinguished
by arranging the 269 data into the same or similar types. The geographical distribution of these 29 types and the corresponding
main climatic features were described. The relations between WI and distribution of these vegetation types were discussed
in detail. As a result, WI values (°C month) corresponding to the vegetation zones could be summarized as follows: (1) arctic
or alpine vegetation zone: 0–15; (2) boreal or subalpine vegetation zone: 15-(50–55); (3) cool-temperate vegetation zone:
(50–55)–(80–90); (4) warm-temperate vegetation zone: (80–90)–(170–180). These values almost coincided with Kira's values.
Chinese postgraduate student in Japan sent by the Chinese Government. 相似文献
948.
Nigel J. Robinson 《Journal of applied phycology》1989,1(1):5-18
Metallothioneins, MT's, are low-molecular-weight, cysteine-rich, polypeptides that complex ‘soft’ metal ions in thiol clusters.
They are structurally diverse. Some MT's are gene products, while others are secondary metabolites. Two of the three classes
of MT have been identified in algae. Eukaryotic algae possess the secondary metabolites referred to as class III MT. There
is no unequivocal evidence that MT genes occur in eukaryotic algae. However, the products of MT genes have been identified
in cyanobacteria. These genes and their metal regulatory elements remain to be isolated and characterized.
MT's have attracted interest from researchers involved in a wide range of disciplines including bioinorganic chemistry, biochemistry,
molecular biology, physiology, toxicology, environmental science and medicine. Although, the precise physiological roles of
these polypeptides remain undefined, a large number of functions have been speculated. These molecules chelate toxic trace
metals, such as Cd, thereby reducing the concentration of cytotoxic, free-metal ions. Furthermore, some MT's are believed
to be involved in zinc and copper homoeostasis. Future studies should reveal whether or not some of the diversity of MT structure
reflects a diversity of function. 相似文献
949.
Summary The release of intact CU(I)8-thionein from copper-resistant copper-loaded yeast cells, strain X 2180-1Aa, has been shown. This copper(I)-thiolate-rich protein was characterized and compared with the chemical and physicochemical properties of intracellular yeast Cu-thionein. The same molecular mass and stoichiometry of 8 mol copper atoms/mol protein was found. No detectable difference between the Cu-thioneins was seen in luminescence emission, electronic absorption in the ultraviolet region, chiroptical data or amino acid composition. The importance of stable Cu(I)-thiolates in Cu-thionein as a safe vehicle for transporting copper in a non-reactive manner is confirmed. 相似文献
950.
P. K. Lauf 《The Journal of membrane biology》1990,118(2):153-159
Summary Hydroxylamine, a potent oxidizing agent used to reverse carbethoxylation of histidine by diethylpyrocarbonate, activated Cl-dependent K flux (KCl cotransport) of low K sheep red blood cells almost sixfold. When KCl cotransport was already stimulated by N-ethylmaleimide, hydroxylamine caused an additional twofold activation suggesting modification of sites different from those thiol alkylated. This conclusion was supported by the finding that hydroxylamine additively augmented also the diamide-induced KCl flux (Lauf, P.K. 1988.J. Membrane Biol.
101:179–188) with dithiothreitol fully reversing the diamide but not the hydroxylamine effect. Stimulation of KCl cotransport by hydroxylamine was completely inhibited by treatment with diethylpyrocarbonate also known to prevent KCl cotransport stimulation by N-ethylmaleimide, both effects being independent of the order of addition. Hence, although the effect of carbethoxy modification on KCl flux cannot be reversed by hydroxylamine and thus excludes histidine as the target for diethylpyrocarbonate, our finding reveals an important chemical determinant of KCl cotransport stimulation by both hydroxylamine oxidation and thiol group alkylation. 相似文献