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41.
In brain tissue a spectrin-like calmodulin-binding protein calspectin, or fodrin, is concentrated in a synaptosome fraction, where most of the calspectin is associated with the synaptic membranes. This endogenous calspectin was phosphorylated by protein kinase system(s) associated with the membranes. Here, we report the solubilization and partial purification of the membrane-associated calspectin kinase activity. The activity was resolved on a gel filtration column into two fractions, peaks I and II having estimated Mr of 800 000 and 88 000. The activity of peak I was dependent on the presence of both Ca2+ and calmodulin. Peak II revealed a basal activity in the absence of Ca2+ and calmodulin, which was stimulated 2-fold by addition of Ca2+. Calmodulin had no effect on the peak II activity. 相似文献
42.
The antimutagenic effect of selenium as sodium selenite, sodium selenate, selenium dioxide, and seleno-methionine was studied
in the AmesSalmonella/microsome mutagenicity test using 7,12-dimethylbenz(a)anthracene (DMBA) and some of its metabolites. Selenium (20 ppm) as
sodium selenite reduced the number of histidine revertants on plates containing up to 100 μg DMBA/plate. Increasing concentrations
of selenium as sodium selenite, sodium selenate, and selenium dioxide up to 40 ppm Se progressively decreased the number of
revertants caused by 50 μg DMBA. DMBA and its metabolites 7-hydroxymethyl-12-methylbenz(a)anthracene, 12-hydroxymethyl-7-methylbenz(a)anthracene,
and 3-hydroxy-7,12-dimethylbenz(a)anthracene were mutagenic forSalmonella typhimurium TA100 in the presence of an S-9 mixture. Selenium supplementation as Na2SeO3 reduced the number of revertants induced by these metabolites to background levels. The antimutagenic effect of inorganic
selenium compounds cannot be explained by toxicity of selenium as determined by viability tests withSalmonella typhimurium TA100. Selenium supplementation in all forms examined, except sodium selenate, decreased the rate of spontaneous reversion.
Selenium as sodium selenate was slightly mutagenic at concentrations of 4 ppm or less. Higher concentration of Na2SeO4 inhibited the mutagenicity of DMBA. The present studies support the anticarcinogenic potential of selenium and indicate that
form and concentration are important factors in this trace element's efficacy. 相似文献
43.
44.
Lipoxygenbase-derived products of arachidonic acid mediate stimulation of hexose uptake in human polymorphonuclear leukocytes 总被引:3,自引:0,他引:3
D A Bass M J Thomas E J Goetzl L R DeChatelet C E McCall 《Biochemical and biophysical research communications》1981,100(1):1-7
The titration of metal-freed bovine α-lactalbumin with Mg2+ ions causes a two-stepped decrease in the tryptophan fluorescence quantum yield and a pronounced spectral shift towards shorter wavelengths, which seems to be a result of the binding of two magnesium ions to the protein molecule. The magnesium binding constants evaluated from the fluorimetric Mg2+-titration are 2·103 and 2·102 M?1. Mg2+ ions in millimolar concentrations almost do not influence the binding of Ca2+ ions to the protein. 相似文献
45.
S. Felter M. Diatewa C. Schneider A.J.C. Stahl 《Biochemical and biophysical research communications》1981,98(3):727-734
Yeast mitochondrial tRNA synthetase has been partially purified and chromatographic, catalytic and antigenic properties have been compared to the cytoplasmic homologous enzyme from yeast. No significant differences could be observed between the two enzymes with respect to their behaviour during ammonium sulfate precipitation or in chromatographic separation on DEAE cellulose, hydroxylapatite and Sephadex G 200. The Km of the two enzymes toward tRNAs from yeast mitochondria, yeast cytoplasm or E. coli are pratically identical. The antigenic properties of the two enzymes are very similar; antisera against either the mitochondria or the cytoplasmic enzyme lead to the inhibition of their catalytic properties. The mitochondrial ValRS is formed by a single polypeptide chain whose molecular weight is 125,000 daltons, a value very close to that of the yeast cytoplasmic enzyme. 相似文献
46.
Marie-Luise Blue David L. Williams 《Biochemical and biophysical research communications》1981,98(3):785-791
Apo II and vitellogenin were detected in sera of nonestrogenized roosters by radioimmunoassay. Tamoxifen (30mg/kg) raised basal serum apo II more than 50 fold and vitellogenin more than 15 fold. Serum accumulation of apo II was biphasic in response to increasing doses of tamoxifen. This biphasic response was reflected in the relative rates of hepatic apo II synthesis. The tamoxifen metabolites, hydroxytamoxifen and desmethyltamoxifen, and the triphenylethylene antiestrogen, CI 628, also increased serum apo II. These studies show that the expression of vitellogenin and apo II genes occurs at a basal rate prior to exogenous estrogen treatment. These experiments also demonstrate that the triphenylethylene antiestrogens have agonist activity in the chicken when very sensitive techniques are used to measure estrogen-regulated proteins. 相似文献
47.
Methjylation in Physarum DNA 总被引:4,自引:0,他引:4
48.
49.
Summary Sodium and chloride influxes across the nonshort-circuited isolated skin ofRana esculenta were measured at widely varying external ionic concentrations.The curve describing sodium transport has two Michaelis-Menten components linked at an inflection point occurring at an external sodium concentration of about 7 meq. Chloride transport can also be represented by two saturating components. A possible explanation of these kinetics is discussed.At sodium concentrations lower than 4 meq it is possible to define a component of the sodium transport mechanism as having a high affinity for sodium and which is independent of the nature of the external anion. A high affinity for chloride of the chloride transport system functioning at low external concentrations is also found but is significantly different from that of sodium. These systems show the physiological characteristics of the countertransports (Na
ext
+
/H
int
+
; Cl
ext
–
/HCO
3int
–
) functioning at low external concentrations.At external concentrations higher than 4 meq a low affinity transporting system in which chloride and sodium are linked superimpose on the high affinity components.The physiological significance of these results is discussed. 相似文献
50.
E S Kang R E Gates T M Chiang A H Kang 《Biochemical and biophysical research communications》1979,86(3):769-778
Intact adipocytes exhibit ectoprotein kinase activity as reflected by their ability to catalyze the transfer of the terminal phosphate of (γ-32P) ATP to histone added to a cell suspension. This activity is substrate, time and cell number dependent. Lineweaver-Burk plots gave Km and Vmax values for ATP of 5 × 10?5 M and 7.14 pmoles/min/1.5 × 105 cells. Cyclic AMP but not cyclic GMP in μM concentrations stimulates ectoprotein kinase activity. The controlled tryptic digestion of intact cells results in reduction of ectoprotein kinase activity. This activity is not due to leakage of intracellular protein kinases during the preparative procedure nor to penetration of histone into the cells. Additional phosphoproteins not accessible to endogenous protein kinase activity are also localized on the external surface of the intact fat cell. 相似文献