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51.
Kinetic studies on formation of cytochrome oxidase of Rhodopseudomonas capsulata after a shift from phototrophic to chemotrophic growth. 总被引:1,自引:1,他引:0 下载免费PDF全文
Rhodopseudomonas capsulata cells were shifted from phototrophic (anaerobic, light) to chemotrophic (semiaerobic, dark, 10% air saturation) growth conditions. During the adaptation period of 4 h, the bacteriochlorophyll content of cells and membranes decreased, and a newly synthesized 65-kilodalton polypeptide of the cytochrome oxidase was incorporated into the membrane fraction. The enzymatic activity of the cytochrome oxidase increased strongly after a lag time of 2 h. The amount of cytochrome oxidase protein does not follow the same kinetics. The relative amount of a membrane-bound cytochrome c of low molecular weight, which has been proposed to be a donor for the cytochrome oxidase, increased during adaptation. 相似文献
52.
The photosynthetic chromatophore membranes of Rhodopseudomonas capsulata were fused with liposomes to investigate the effects of lipid dilution on energy transfer between the bacteriochlorophyll-protein complexes of this membrane. Phosphatidylcholine-containing liposomes were mixed with chromatophores at pH 6.0 to 6.2, and the mixture was fractionated on discontinuous sucrose gradients into four membrane fractions with lipid-to-protein ratios that varied 11-fold. Freeze-fracture electron microscopy revealed that the fractions contained closed vesicles formed by the fusion of liposomes to chromatophores. Particles with 9-nm diameters on the P fracture faces did not appear to change in size with increasing lipid content, but the number of particles per membrane area decreased proportionally with increases in the lipid-to-protein ratio. The bacteriochlorophyll-to-protein ratios, electrophoretic polypeptide profiles on sodium dodecyl sulfate-polyacrylamide gels, and light-induced absorbance changes at 595 nm caused by photosynthetic reaction centers were not altered by fusion. The relative fluorescence emission intensities due to the B875 light-harvesting complex increased significantly with increasing lipid content, but no increases in fluorescence due to the B800-B850 light-harvesting complex were observed. Electron transport rates, measured as succinate-cytochrome c reductase activities, decreased with increased lipid content. The results indicate an uncoupling of energy transfer between the B875 light-harvesting and reaction center complexes with lipid dilution of the chromatophore membrane. 相似文献
53.
Temporal Profiles of Proteins Responsive to Transient Ischemia 总被引:4,自引:3,他引:1
The responses of long and short half-lived proteins to ischemia were measured in rat brain during 6 days of recovery from 30 min of transient forebrain ischemia produced by four-vessel occlusion. At the end of the ischemic interval, the neocortical activities of four vulnerable enzymes [ornithine (ODC) and S-adenosylmethionine (SAMDC) decarboxylases, and RNA polymerases I and II] were unchanged, but within 30 min of reperfusion, their activities dropped by 25-50%. The loss of substance P in the striatum and substantia nigra was slower, reaching about 50% by 12 h. On the other hand, the activities of 5 long half-lived enzymes did not change in the neocortex at 5 and 15 h of reperfusion and regional protein concentrations were essentially unaffected over 6 days survival. The rate and extent of normalization of the amounts or activities of the vulnerable proteins varied. RNA polymerase II and ODC activities were restored within 4 h, and ODC showed a biphasic increase in activity, with peaks at 10 h and 2-3 days. RNA polymerase I and SAMDC activities were restored by 18 h and 5 days, respectively, whereas substance P concentrations did not completely recover, even at 6-15 days. The greater the regional reduction of blood flow during ischemia, the larger the net change (gain or loss) of SAMDC or ODC activity and the longer the time required to normalize the activities of these enzymes. The average rate of proteolysis, assessed by measuring the rate of clearance of 14C from protein prelabeled with [14C]bicarbonate, was abnormal during the first 2 days of reperfusion. Postischemic changes in both protein synthesis and degradation could affect the amounts of some of the proteins responsive to transient ischemia. 相似文献
54.
Deprenyl Protects Dopamine Neurons from the Neurotoxic Effect of 1-Methyl-4-Phenylpyridinium Ion 总被引:3,自引:2,他引:1
1-Methyl-4-phenylpyridinium ion (MPP+) is the product of the metabolic oxidation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) by monoamine oxidase (MAO). MPP+ is toxic to 3,4-dihydroxyphenylethylamine (dopamine, DA) neurons in explant cultures of rat embryonic midbrain. Addition of 2.5 microM MPP+ to the feeding medium for 6 days results in significant reduction of the DA levels in the cultures (to 19% of control) as well as in the uptake of [3H]DA (to 32% of control). When the cultures are treated with the MAO inhibitor deprenyl (10 microM) 24 h prior to and during exposure to MPP+, the DA neurons are protected from the toxicity of the drug. In the combined deprenyl plus MPP+ treatment, the levels of DA in the cultures remain at the control range and the [3H]DA uptake is reduced to only 73% of control. These results indicate that MAO is involved in the toxicity of MPP+ on DA neurons. 相似文献
55.
Gerald D. Fasman 《Journal of biosciences》1985,8(1-2):15-23
The Chou-Fasman predictive algorithm for determining the secondary structure of proteins from the primary sequence is reviewed.
Many examples of its use are presented which illustrate its wide applicability, such as predicting (a) regions with the potential
for conformational change, (b) sequences which are capable of assuming several conformations in different environments, (c)
effects of single amino acid mutations, (d) amino acid replacements in synthesis of peptides to bring about a change in conformation,
(e) guide to the synthesis of polypeptides with definitive secondary structure,e.g. signal sequences, (f) conformational homologues from varying sequences and (g) the amino acid requirements for amphiphilicα-helical peptides. 相似文献
56.
Dr. G. Schleicher W. E. Stumpf U. Drews K. U. Thiedemann M. Sar 《Histochemistry and cell biology》1985,82(5):453-461
Summary The distribution of specific nuclear binding sites for androgens and estrogens in the male accessory sex organs of the mouse
was assessed by autoradiography with3H dihydrotestosterone (3H DHT) and3H estradiol (3H E2).
With3H DHT nuclear labeling differed among the epithelia of the organs. It was high in seminal vesicle and ampullary gland, moderate
in ventral prostate, urethral gland, prostatic excretory ducts and the ampulla ductus deferentis, low in dorsal prostate and
low or absent in coagulation gland. With3H E2, in contrast, epithelial nuclear labeling was high only in coagulation gland, moderate or low in seminal vesicle, low or
absent in ventral and dorsal prostate and absent in ampullary gland and ampulla ductus deferentis. In the lamina propria of
all organs nuclear labeling with3H DHT was generally moderate and existed only in some cells, with the highest number in the ampulla ductus deferentis. With3H E2, nuclear labeling in the lamina propria showed a high intensity in all organs, except in ventral and dorsal prostate which
remained unlabeled. Many labeled cells were found in the deferent duct and its ampulla, while in the other organs only a few
cells showed nuclear labeling with3H E2. In the smooth muscle sheath of all organs, some muscle cells were moderately labeled with3H DHT, but not with3H E2.
The results indicate the presence of nuclear receptors in male accessory sex organs for both dihydrotestosterone and estradiol.
The differential patterns of3H DHT and3H E2 nuclear uptake suggest differential sensitivities of the individual organs and their tissue compartments for androgens and
estrogens.
Supported by PHS grant NSO9914 to W.E.S. and Deutsche Forschungsgemeinschaft Dr94/4 to U.D. The work of Dr. Schleicher and
his stay in Chapel Hill were additionally sponsored by Studienstiftung des Deutschen Volkes and Boehringer-Ingelheim Fonds 相似文献
57.
Gerald S. Manning 《Cell biochemistry and biophysics》1985,7(3):177-184
The equilibrium trajectory of the axis of a rod subject to an externally imposed curved potential energy trough tends to conform
to the shape of the curved trough, but also tends to be straight because of elastic resistance to bending. The actual path
of the axis is a balance between the two extremes. We consider a potential energy trough centered along a circular arc of
radiusR. For a rod of small length compared toR, we show that the axis at equilibrium forms an arc of a circle of radius greater thanR. The value of the radius of the axial path depends on the relative values of the Hooke’s Law bending constant for the rod
and the depth and width of the trough. Motivation for the calculation is provided by nucleosomal DNA, which conforms to the
surface of a roughtly cylindrical histone core at physiological ionic strength, but is observed to unwind into a partially
extended conformation at very low ionic strength. We suggest that the rigidity to bending of short DNA segments becomes sufficiently
great at low ionic strength to overcome attractive interactions with the histone surface. Alternately, of course, if during
the cell cycle mutually attractive forces between DNA and histone core are weakened at constant ionic strength, the same type
of unfolding would be expected to occur as the strength of the DNA-histone contacts drops below the level required to overcome
elastic resistance to bending of the DNA rod. 相似文献
58.
The effects of mineral salts constituting water hardness on fecundity ofDaphnia magna were assessed. Of the salts tested, increased concentrations of NaHCO3 and MgSO4 had no effect on fecundity, CaSO4 significantly increased fecundity, and KCl significantly reduced fecundity. The number of offspring produced per daphnid
was correlative to the CaSO4 concentration at CaSO4 concentrations between 91 and 2100 mg/ℓ. The effects of CaSO4 on daphnid fecundity could influence the interpretive outcome of industrial wastewater toxicity tests using this species
when the waste and dilution waters contain different concentrations of CaSO4. It is recommended that when performing these tests, dilution water be sampled at the intake site of the industry's water
source, thus assuring initial comparability of the waste and dilution waters. The CaSO4 content of the water prior to and after industrial use should be determined to identify any alterations of CaSO4 concentration during use. Identification of CaSO4 concentration differences can aid in the interpretation of effects associated with the wastewater. 相似文献
59.
C. Lal Kapoor Gerald J. Chader 《Biochemical and biophysical research communications》1984,122(3):1397-1403
A calcium phospholipid-dependent protein kinase (C-kinase) activity was detected in the soluble fraction of rod outer segments (ROS) of the bovine retina. The enzyme required calcium, phosphatidylserine (PS) and diacylglycerol for maximal activity. In the presence of calcium and PS, C-kinase endogenously phosphorylated proteins with molecular weights of 95,000, 91,000, 31,000, 21,000, 19,000, 18,000, 16,000, 14,000 and 11,000. Addition of diolein in the reaction mixture further enhanced the endogenous phosphorylation of these proteins. Retinal was found to inhibit the phosphorylation of endogenous proteins by C-kinase in a concentration dependent manner. Half-maximal inhibition of enzyme activity was obtained at a retinal concentration of about 12μM. These results suggest that calcium, phospholipids and the C-kinase enzyme may play an important role in the functional regulation of rod photoreceptors and, with retinal, perhaps in the visual process as well. 相似文献
60.
Jef D. Boeke Francois La Croute Gerald R. Fink 《Molecular & general genetics : MGG》1984,197(2):345-346
Summary Mutations at the URA3 locus of Saccharomyces cerevisiae can be obtained by a positive selection. Wild-type strains of yeast (or ura3 mutant strains containing a plasmid-borne URA3
+ gene) are unable to grow on medium containing the pyrimidine analog 5-fluoro-orotic acid, whereas ura3
– mutants grow normally. This selection, based on the loss of orotidine-5-phosphate decarboxylase activity seems applicable to a variety of eucaryotic and procaryotic cells. 相似文献