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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The glycosylphosphatidylinositol membrane anchor of variant surface glycoprotein of the African trypanosome Trypanosoma brucei contains several mannosyl residues for which dolichol phosphoryl mannose is supposed to be the precursor; this itself is probably synthesised by a dolichol-dependent mannosyltransferase. We have characterised and localised a mannosyltransferase activity of T. brucei which transfers mannose from GDP-[14C]mannose to exogenously added dolichyl phosphate. The enzyme was saturable for both its substrates and had a Km of 7.8 microM and 3.3 microM, respectively, for dolichyl phosphate and GDP-mannose. Mannosyltransferase was labile at 37 degrees C in the presence of Triton X-100, but its activity remained constant for at least 60 min at temperatures between 10-15 degrees C. The enzyme was inhibited by amphomycin and this inhibition was potentiated by the presence of 10 mM CaCl2. After subcellular fractionation of cell homogenates by differential centrifugation, mannosyltransferase was recovered mainly in the microsomal fraction and its distribution was very similar to that of RNA, a marker for the rough endoplasmic reticulum. After isopycnic centrifugation in a linear sucrose gradient the distribution of mannosyltransferase also resembled that of RNA. Both constituents exhibited a shift towards lower densities after pre-treatment of microsomal membranes with inorganic pyrophosphate, while other membrane markers such as acid phosphatase and nucleoside diphosphatase did not. It is concluded that the formation of dolichol phosphoryl mannose from GDP-mannose and dolichyl phosphate in T. brucei occurs mainly in the rough endoplasmic reticulum.
Mol Biochem Parasitol 1994 Feb
PMID:Possible localisation of dolichol-dependent mannosyltransferase of Trypanosoma brucei to the rough endoplasmic reticulum. 751 92

By establishing a unique screening method, we have isolated yeast mutants that die only after differentiating into cells with a mating projection, and some of them are also defective in Ca2+ signaling. The mutants were classified into five complementation groups, one of which we studied extensively. This mutation defines a new gene, designated MID1, which encodes an N-glycosylated, integral plasma membrane protein with 548 amino acid residues. The mid1-1 mutant has low Ca2+ uptake activity, loses viability after receiving mating pheromones, and escapes death when incubated with high concentrations of CaCl2. The MID1 gene is nonessential for vegetative growth. The efficiency of mating between MATa mid1-1 and MAT alpha mid1-1 cells is low. These results demonstrate that MID1 is required for Ca2+ influx and mating.
Mol Cell Biol 1994 Dec
PMID:MID1, a novel Saccharomyces cerevisiae gene encoding a plasma membrane protein, is required for Ca2+ influx and mating. 752 55

Glutathione (GSH) regeneration was studied in rabbit erythrocytes which were loaded with calcium using ionophore A23187. Calcium-loading induced by A23187 and various concentrations of CaCl2 caused a dose-dependent depression in red cell GSH regeneration. The lowered GSH regeneration was mainly due to reduction of ATP level. In an experiment using haemolysate, the effect of calcium per se was negligible, while magnesium strongly affected GSH regeneration by controlling the rate of hexokinase reaction. These results indicate a possibility that cation perturbation, metabolic decay and oxidative damage are all interrelated in the erythrocyte aging process.
Comp Biochem Physiol B Biochem Mol Biol
PMID:Glutathione regeneration in calcium-loaded erythrocytes: a possible relationship among calcium accumulation, ATP decrement and oxidative damage. 755 47

We have shown previously that a chronic treatment with glucocorticoids enhances cAMP- or ACTH-induced steroidogenesis of cultured ovine adrenocortical cells. This effect appears to involve a greater amount of cholesterol in mitochondria. Hence, the present study aimed to define the role of glucocorticoids in cholesterol metabolism by these cells. 2-day-old cultures were exposed to different hormones or inhibitors (10(-6) M ACTH, 10(-5) M metyrapone) for 28-48 h. At the end of the treatment period, the cells were stimulated for 2 h with 10(-3) M 8Br-cAMP, in the presence of 10(-3) M aminoglutethimide (in order to load mitochondria with cholesterol). Mitochondria were then isolated and incubated without or with 100 microM cholesterol either in the presence or absence of 10(-3) M CaCl2, or with 25 microM 22R-hydroxycholesterol. Mitochondria isolated from dexamethasone-treated cells produced consistently more pregnenolone than mitochondria from control cells, suggesting that at least part of the additional cholesterol present in these mitochondria was available for steroidogenesis. However, similar differences were obtained when mitochondria were incubated in the presence of exogenous cholesterol, both with or without calcium, or in the presence of 22R-hydroxycholesterol. Pregnenolone production under these latter conditions was much higher than when endogenous cholesterol was the only substrate. Conversely, metyrapone treatment of the cells resulted in lower production of pregnenolone from 22R-hydroxycholesterol by their mitochondria. Likewise ACTH treatment enhanced pregnenolone production by isolated mitochondria irrespective of the incubation conditions. These effects of dexamethasone and ACTH were not related to higher amounts of adrenodoxin, adrenodoxin reductase or cytochrome P450scc. These results indicate that exposure of ovine adrenocortical cells to glucocorticoids or ACTH enhances their steroidogenic potency not only by increasing the amount of cholesterol available for steroidogenesis but also by enhancing some step(s) involved in the transformation of cholesterol into pregnenolone.
J Steroid Biochem Mol Biol 1995 Oct
PMID:Glucocorticoids enhance the cholesterol side-chain cleavage activity of ovine adrenocortical mitochondria. 757 21

An exo-polygalacturonase with an isoelectric point of 4.6 and an apparent molecular weight of 45 kDa was isolated from apple tissue decayed by Botrytis cinerea. This isozyme had a similar isoelectric point, optimum pH, and mode of action as an isozyme produced in liquid culture by B. cinerea. The enzyme produced in the decayed tissue was less sensitive to lower pH and less inhibited by CaCl2, MgCl2, or NaCl than the enzyme produced in culture. Such changes in the properties of the enzyme produced in infected tissue could have been essential for the pathogen's successful colonization of the host tissue. Among the cations studied, calcium was the best inhibitor of PG activity.
Biochem Mol Biol Int 1995 Apr
PMID:Polygalacturonase produced in apple tissue decayed by Botrytis cinerea. 762 31

We examined the influence of calcium on neurotoxicity of AlCl3 and Al-lactate toward differentiated NB2a/d1 cells. Apart from induction of perikaryal neurofibrillary inclusions, AlCl3 at 1 mM induced no obvious additional signs of toxicity when added to culture medium in the presence of the normal medium CaCl2 content of 1.8 mM, nor when extracellular calcium was decreased by the addition to the medium of 0.9 mM EDTA. Increasing the extracellular CaCl2 concentration by fivefold was only marginally toxic, but in the presence of AlCl3, reduced viable cell numbers by well over 50% as compared to control cultures, and by approximately 50% vs fivefold CaCl2 alone. A twofold increase in extracellular CaCl2 did not increase the percentage of cells exhibiting Bielschowsky-positive perikarya, but induced a near doubling in the percentage of cells exhibiting accumulations in the presence of 1 mM Al-lactate. AlCl3 (1 mM) retards the electrophoretic migration of NF subunits on SDS-gels. This effect was eliminated by withholding CaCl2 from the incubation mixture and including 5 mM EDTA during incubation of cytoskeletons with AlCl3. The presence of CaCl2 alone did not alter NF migration. These findings underscore the possibility that multiple factors, including those that compromise general neuronal homeostasis, may contribute to neurofibrillary pathology.
Mol Chem Neuropathol
PMID:Calcium modulates aluminum neurotoxicity and interaction with neurofilaments. 763 19

The energy-transducing nicotinamide nucleotide transhydrogenase of Rhodospirillum rubrum is composed of 3 subunits alpha 1, alpha 2 and beta, with M(r) values, respectively, of 40.3, 14.9 and 47.8 kDa. Subunit alpha 1 is water-soluble, loosely bound to chromatophores, and can be easily and reversibly removed. Subunits alpha 2 and beta are integral membrane proteins, and their removal from chromatophores requires the use of detergents. Treatment of chromatophores with various detergents inhibited reconstitution of transhydrogenase activity when alpha 1 was added to the detergent-treated chromatophores. This apparent inhibition could be reversed by addition of a divalent metal ion. The best condition for extraction of alpha 2/beta from chromatophores was the use of 1% deoxycholate in the presence of 0.34 M KCl. Under these conditions, the extracted alpha 2/beta mixed with purified alpha 1 was completely inactive, but gained full activity when the assay medium was supplemented with 2-3 mM MgCl2 or CaCl2. It was shown that metal ions had little effect on the apparent Km of substrates, but greatly increased the affinity between purified alpha 1 and the detergent-treated or detergent-solubilized alpha 2/beta. It seems possible that the R. rubrum transhydrogenase contains a detergent-extractable metal ion, which is required for proper binding of the soluble alpha 1 subunit to the chromatophore-bound alpha 2/beta subunits.
Biochem Mol Biol Int 1994 Dec
PMID:Studies on reconstitution of the Rhodospirillum rubrum nicotinamide nucleotide transhydrogenase. 769 82

A common strongly ordered multi-step-pattern of endogenous DNA degradation was induced in rat liver nuclei and intact thymocytes, prepared in the presence of chelating agents and incubated in the presence of CaCl2 and/or MgCl2. It consisted of sequential generation of 0.3 Mbp, then 0.05 Mbp DNA fragments and finally of oligo- and mononucleosomal DNA. Oligonucleosomal DNA was generated when the genome had already been disintegrated into 0.05 Mbp DNA fragments. ZnCl2 completely inhibited advanced genome cleavage to oligo- and mononucleosomal DNA without affecting the initial generation of large DNA fragments. Therefore, the endonucleolytic activity which produce large DNA fragments is different from Ca2+/Mg2+ endonuclease. The similar pattern of DNA degradation was observed in thymocytes treated with dexamethasone and with the topoisomerase II inhibitor VM-26, the agents known to induce apoptosis. The effect of VM-26 strongly suggests the involvement of topoisomerase II in generation of large DNA fragments. Multi-level organization and regulation of the chromatin structure determine the stepwise process of genome degradation. Detachment of chromatin from the nuclear matrix attachment regions may be one of the possible mechanisms of switching off the genome function and triggering the multi-step process of endogenous chromatin degradation thus leading to cell death in terminal differentiation or stress-induced apoptosis.
Comp Biochem Physiol B Biochem Mol Biol 1995 May
PMID:Comparative study of induction of endogenous DNA degradation in rat liver nuclei and intact thymocytes. 774 35

Oscillation patterns of the oxygen yield per flash induced by a train of single-turnover flashes were measured as a function of dark incubation and different pre-illumination conditions in several autotrophic mutant strains of Synechocystis sp. PCC 6803 carrying short deletions within the large, lumen-exposed hydrophilic region (loop E) of the chlorophyll a-binding photosystem II protein CP47. A physiological and biochemical characterization of these mutant strains has been presented previously [Eaton-Rye, J. J., & Vermaas, W. F. J. (1991) Plant Mol. Biol. 17, 1165-1177; Haag, E., Eaton-Rye, J. J., Renger, G., & Vermaas, W. F. J. (1993) Biochemistry 32, 4444-4454], and some functional properties were described recently [Gleiter, H. M., Haag, E., Shen, J.-R., Eaton-Rye, J. J., Inoue, Y., Vermaas, W. F. J., & Renger, G. (1994) Biochemistry 33, 12063-12071]. The present study shows that in several mutants the water-oxidizing complex (WOC) became inactivated during prolonged dark incubation, whereas the WOC of the wild-type strain remained active. The rate and extent of the inactivation in the mutants depend on the domain of loop E, where 3-8 amino acid residues were deleted. The most pronounced effects are observed in mutants delta(A373-D380) and delta(R384-V392). A competent WOC can be restored from the fully inactivated state by illumination with short saturating flashes. The number of flashes required for this process strongly depends on the site at which a deletion has been introduced into loop E. Again, the most prominent effects were found in mutants delta(A373-D380) and delta(R384-V392). Interestingly, the number of flashes required for activation was reduced by more than an order of magnitude in both mutants by the addition of 10 mM CaCl2 to the cell suspension. On the basis of a model for photoactivation proposed by Tamura and Cheniae (1987) [Biochim. Biophys. Acta 890, 179-194], a scheme is presented for the processes of dark inactivation and photoactivation in these mutants. The results presented here corroborate an important role of the large hydrophilic domain (loop E) of CP47 in a functional and stable WOC.
 ...
PMID:Involvement of the CP47 protein in stabilization and photoactivation of a functional water-oxidizing complex in the cyanobacterium Synechocystis sp. PCC 6803. 775 15

The present study investigated the role of intracellular Ca2+ (Ca2+i) elevation on the inactivation of maturation promoting factor (MPF) in rabbit oocytes. The effects of the number of Ca2+ stimulations and of the amplitude of Ca2+i elevation on the profile of histone H1 kinase activity were determined. A Ca2+ stimulation consisted of transferring mature oocytes from culture medium to 0.3 M mannitol containing 0.1-1.0 mM CaCl2, and pulsing them at 1.25 kV/cm for 10 microseconds, or microinjecting 2-8 mM CaCl2 into the oocyte cytoplasm. The number of electrically-induced Ca2+ stimulations was varied, and amplitude of the Ca2+i rise was controlled by altering Ca2+ concentration in the pulsing medium or the injection pipette. Ca2+i concentration was determined with fura-2 dextran; oocytes were snap-frozen at indicated time points and assayed for H1 kinase activity. The activity was quantified by densitometry and expressed as a fraction of activity in nonstimulated oocytes. Electrically-mediated Ca2+i rises inactivated H1 kinase in a manner dependent on the number of Ca2+ stimulations. A single Ca2+ stimulation inactivated H1 kinase to 30-40% of its initial activity. However, H1 kinase inactivation was only transient, regardless of the amplitude of the electrically- or injection-mediated Ca2+i elevation. Increasing the number of Ca2+ stimulations helped to maintain H1 kinase activity at basal (pronuclear) levels. The results show the necessity of a threshold of Ca2+i concentration to trigger MPF inactivation, and suggest a role for the extended period of time over which Ca2+i oscillates at fertilization.
Mol Reprod Dev 1995 Feb
PMID:Inactivation of histone H1 kinase by Ca2+ in rabbit oocytes. 776 19


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