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1.
J A Post J Leunissen-Bijvelt T J Ruigrok A J Verkleij 《Biochimica et biophysica acta》1985,845(1):119-123
Isolated rabbit hearts were perfused by the Langendorff technique, made ischemic and subsequently reperfused. It was found that ischemia results in: (i) aggregation of the intramembranous particles in the sarcolemma and (ii) extrusion of pure lipidic multilamellar structures (liposomes) from swollen mitochondria. Subsequent reperfusion resulted in further aggregation of the sarcolemmal intramembranous particles and disruption of the sarcolemma, which was attended by the formation of liposome-like structures. Intramembrane particle aggregation is explained in terms of lateral phase separation of the membrane lipids and a reduction of repulsive forces between the membrane proteins, both induced by a decrease in pH and an increase in Ca2+ concentration intracellularly. The formation and extrusion of the multilamellar structures are discussed in terms of destabilization of the bilayer which results in a structural blebbing-off of pure lipid. 相似文献
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3.
C B Post 《Journal of molecular biology》1992,224(4):1087-1101
Dynamic averaging effects from internal motions on interproton distances estimated from nuclear Overhauser effects (NOE) are determined by using a molecular dynamics simulation of lysozyme. Generalized order parameters measuring angular averaging and radial averaging parameters are calculated. The product of these two parameters describes the full averaging effects on cross-relaxation. Analysis of 2778 non-methyl NOE interactions from the protein interior and surface indicates that distances estimated by assuming a rigid molecule have less than 10% error for 89% of the NOE interactions. However, analysis of 1854 methyl interactions found that only 68% of the distances estimated from cross-relaxation rates would have less than 10% error. Qualitative evaluation of distances according to strong, medium and weak NOE intensities, when used to define only the upper bound for interproton separation, would misassign less than 1% of the distance constraints because of motional averaging. Internal motions do not obscure the identification of secondary structure, although some instances of significant averaging effects were found for interactions in alpha-helical regions. Interresidue NOEs for amino acids more than three residues apart in the primary sequence are more extensively averaged than intraresidue or short-range interresidue NOEs. Intraresidue interactions exhibit a greater degree of angular averaging than those involving interresidue proton pairs. An internal motion does not equally affect all NOE interactions for a particular proton. Thus, incorporation of averaging parameters in nuclear magnetic resonance structure determination procedures must be made on a proton-pair-wise basis. On the basis of the motional averaging results, particular fixed-distance proton pairs in proteins are suggested for use as distance references. A small percentage of NOE pairs localized to three regions of the protein exhibit extreme averaging effects from internal motions. The regions and types of motions involved are described. 相似文献
4.
A kidney from the budgerigar (budgie, parakeet; Melopsittacus undulatus) is composed of cortical reptilian-type nephrons (without loops of Henle) and mammalian-type nephrons (with loops) grouped together in medullary cones. The loop of the mammalian-type nephrons has a descending segment composed of thin and highly interdigitated cells. These thin limb cells have few mitochondria (15% of cell volume), undetectable Na+,K(+)-ATPase activity, and virtually no basolateral surface amplification. Prior to the hairpin turn, the descending limb thickens, but the cells continue to lack basolateral amplification. Cells just prior to and within the hairpin turn resemble cells of the entire ascending limb. These cells are thick (there is no thin ascending segment in the avian loop), with extensive infoldings of the basolateral membrane surrounding numerous mitochondria (45% of cell volume). The area of basolateral membrane is 25 times that of the apical membrane. The basolateral membrane (but not the apical membrane) is enriched in Na+,K(+)-ATPase activity. The structure of the avian mammalian-type nephron (as epitomized by the budgie nephron) and the fact that NaCl accounts for over 90% of the osmotic activity of avian urine leads to the conclusion that the countercurrent multiplier of the avian kidney functions by active NaCl transport from the entire ascending limb. No explanation is offered for the transport specializations found in the thick descending segment of the loop, just prior to the hairpin turn. 相似文献
5.
A patent foramen ovale is a common intracardiac finding that is located between the left and right atrium. It can cause right-to-left shunting and has a high prevalence in patients who suffer a cryptogenic stroke. Earlier trials did not show superiority of percutaneous patent foramen ovale closure with standard medical therapy over standard medical therapy alone in the treatment of cryptogenic stroke. Interestingly, several meta-analyses show positive results regarding closure, suggesting underpowering of the individual trials. Recently, two large prospective trials and one long-term follow-up study showed benefit of percutaneous closure over standard medical therapy in treatment of cryptogenic stroke. A larger right-to-left shunt or the presence of an atrial septal aneurysm were predictors for a recurrent event. Therefore, percutaneous patent foramen ovale closure after cryptogenic stroke should be recommended over antiplatelet therapy alone in patients younger than 55 years of age with a high-risk patent foramen ovale. 相似文献
6.
K M Sinjorgo T B Hakvoort I Durak J W Draijer J K Post A O Muijsers 《Biochimica et biophysica acta》1987,890(2):144-150
Human cytochrome c oxidase was isolated in an active form from heart and from skeletal muscle by a fast, small-scale isolation method. The procedure involves differential solubilisation of the oxidase from mitochondrial fragments by laurylmaltoside and KCl, followed by size-exclusion high-performance liquid chromatography. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate showed differences between the subunit VI region of cytochrome c oxidases from human heart and skeletal muscle, suggesting different isoenzyme forms in the two organs. This finding might be of importance in explaining mitochondrial myopathy which shows a deficiency of cytochrome c oxidase in skeletal muscle only. In SDS polyacrylamide gel electrophoresis most human cytochrome c oxidase subunits migrated differently from their bovine counterparts. However, the position of subunits III and IV was the same in the human and in the bovine enzymes. The much higher mobility of human cytochrome c oxidase subunit II is explained by a greater hydrophobicity of this polypeptide than of that of the subunit II of the bovine enzyme. 相似文献
7.
Functional Analysis of the Photosynthetic Apparatus of Prochlorothrix hollandica (Prochlorales), a Chlorophyll b Containing Procaryote 总被引:1,自引:0,他引:1
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Light-shade adaptation of the chlorophyll a/b containing procaryote Prochlorothrix hollandica was studied in semicontinuous cultures adapted to 8, 80 and 200 μmole quanta per square meter per second. Chlorophyll a contents based on dry weight differed by a factor of 6 and chlorophyll b by a factor of 2.5 between the two extreme light conditions. Light utilization efficiencies determined from photosynthesis response curves were found to decrease in low light grown cultures due to lower light harvesting efficiencies; quantum requirements were constant at limiting and saturating irradiances for growth. At saturating growth irradiances, changes in light saturated oxygen evolution rate originated from changes in chlorophyll a antenna relative to the number of reaction centers II. At light-limiting conditions both the number of reaction centers II and the antenna size changed. The amount of chlorophyll b relative to reaction center II remained constant. As in cyanobacteria, the ratio of reaction center I to reaction center II was modulated during light-shade adaptation. On the other hand, time constants for photosynthetic electron transport (4 milliseconds) were low as observed in green algae and diatoms. The occurrence of state one to two and state two to one transitions is reported here. Another feature linking photosynthetic electron transport in P. hollandica to that in the eucaryotic photosynthetic apparatus was blockage of the state one to two transition by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Although chlorophyll b was reported in association with photosystem I, the 630 nanometer light effect does not exclude that chlorophyll b is the photoreceptor for the state one to two transition. 相似文献
8.
Inhibition and labeling of sodium, potassium ATPase by the dialdehyde derivative of ATP 总被引:1,自引:0,他引:1
Canine renal Na,K-ATPase was treated with ATP dialdehyde, "oxATP" (20 microM), as described by G. Ponzio, B. Rossi, and M. Lazdunski (1983, J. Biol. Chem. 258, 8201-8205). In this system, a by-product, formaldehyde, was the inactivator. We modified the system to minimize such inhibition and to speed up the reaction. oxATP itself inactivated the enzyme at a rate that was slow at first and later speeded up. We fitted a precursor-product model to the data. Labeling with [3H]oxATP indicated about three sites per alpha beta protomer at complete inactivation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the labeled enzyme showed radioactivity in many components, in the alpha and beta subunits and in small molecules at the tracker dye region. ATP (20 mM) prevented all labeling and inactivation. Ponzio et al. concluded that oxATP labels covalently an ATP binding site. Our experiments did not support this conclusion. Ouabain did not affect labeling. Sodium stimulated both inhibition and labeling more than potassium did, indicating a high-affinity ATP binding site, if any. But nucleotide specificity for preventing or producing inhibition did not correspond to nucleotide specificity for binding of ATP to the native enzyme. Blocking the ATP binding center with fluorescein isothiocyanate or fluorosulfonyl benzoyl adenosine had no effect on [3H]oxATP labeling. ATP also prevented [3H]oxATP labeling of bovine serum albumin or of integral-membrane proteins. 相似文献
9.
Adele Post 《Polar Biology》1990,10(4):241-245
Summary Variation in leaf pigmentation from green to ginger is observed for Ceratodon purpureus (Hedw.) Brid. in Antarctica. Electron microscopy of ginger and green leaves reveals less thylakoid stacking, a response to greater light exposure, in the ginger leaves. In extremely exposed sites C. purpureus has low chlorophyll a/b ratios which correlate with decreased 77K chlorophyll fluorescence, indicating damage to chlorophyll a. Pigment analysis of ginger moss shows that even when the chlorophyll a/b ratio has not decreased the pigment composition differs from green moss. The increase in anthocyanin and decrease in chlorophyll concentrations largely account for the visual change from green to ginger. The ratio of total carotenoid to chlorophyll varies from 0.35 in green moss to 0.55 in the ginger moss, with violaxanthin increased preferentially. Since these changes in pigmentation are consistent with photoprotection and they are linked to light dependent variations in chloroplast structure, it appears that photoprotective pigments are a useful adaptation for the bright Antarctic environment. 相似文献
10.
Transitions in the growth limiting factor from light (I) to nitrogen (N) and vice versa caused changes in geosmin production, protein and carbohydrate content, and the synthesis of pigments such as chlorophyll a (Chl a), phycobiliproteins (PBPs), and -carotene of the cyanobacterium Oscillatoria brevis. Following IN transition the first 150h, the decrease in protein content was compensated for by an increase of carbohydrates, and thereby, a constant biomass level was maintained in this period. Thereafter, biimass dropped to 15% of its initial level. A decrease in geosmin and pigment content was observed during transition from IN-limited growth. However, geosmin increased relative to phytol (Chl a) and -carotene which may indicate that a lowered demand for phytol and -carotene during N-limited growth allows isoprenoid precursors to be directed to geosmin rather than to pigment synthesis. Synthesis of Chl a and -carotene at the expense of geosmin was suggested for the observed start of increase in geosmin production only at the time that Chl a and -carotene had reached their I-limited steady state. Transition from nitrogen to light limited growth caused an acceleration of metabolism shown by a rapid decrease in carbohydrate content accompanied by an increase in protein content. The growth rate of the organisms temporarily exceeded the dilution rate of the culture and the biomass level increased 6-fold. Due to the only modest changes in geosmin production (2-fold) compared to changes in biomass level (6-fold) during I-or N-limited growth, environmental factors seem to have limited effect on geosmin production.Abbreviations Chl a
chlorophyll a
- dry wt
dry weight;
- I-limited
light-limited
- N-limited
nitrogen-limited
- PBP
phycobiliprotein
This research was performed at the Department of Microbiology, University of Amsterdam, with finacial support provided by the Royal Norwegian Ministry of Foreign Affairs and the Royal Norwegian Council for Scientific and Industrial Research 相似文献