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1.
2.
Ca2+ is an important intracellular messenger affecting many diverse processes. In eukaryotic cells, Ca2+ storage is achieved within specific intracellular organelles, especially the endoplasmic/sarcoplasmic reticulum, in which Ca2+ is buffered by specific proteins known as Ca2+ buffers. Ca2+ buffers are a diverse group of proteins, varying in their affinities and capacities for Ca2+, but they typically also carry out other functions within the cell. The wide range of organelles containing Ca2+ and the evidence supporting cross-talk between these organelles suggest the existence of a dynamic network of organellar Ca2+ signaling, mediated by a variety of organellar Ca2+ buffers. 相似文献
3.
It is now well established that calreticulin is a high capacity Ca(2+)-binding protein which is a major Ca2+ storage protein of the lumen of endoplasmic reticulum membranes in a wide variety of tissues with the exception of skeletal and cardiac muscles. However, in nervous tissue, confusion exists regarding the nature of the intracellular Ca2+ stores, as the organelle responsible for Ca2+ storage has been identified as the endoplasmic reticulum by some investigators and as the specialized organelle, calciosome by others. Calreticulin, calsequestrin, and calsequestrin-like proteins have all been, on different occasions, reported to be present in calciosomes. Cerebral and cerebellar tissues, moreover, have been shown to contain somewhat different systems of Ca(2+)-buffering proteins. In the present paper we discuss evidence that the Ca2+ storage systems of the retina may prove to be more complex than those of other neuronal tissues. Biochemical and immunocytochemical evidence indicates the presence of either an isoform of calreticulin or another protein that is antigenically similar to calreticulin, but of slightly higher molecular weight, in the endoplasmic reticulum of both neurons and Müller glia from rabbit neural retina. However, as retinal neurons express Purkinje cell markers, one may expect to observe the presence of calsequestrin in these cells as well. Secondly, antibodies against the onchocercal RAL-1 antigen recognize a protein sharing 62-65% amino acid sequence identity with calreticulin. The anti-RAL-1 antibodies show specificity for the retina. Whether or not the RAL-1 antigen is an active part of the Ca2+ storage systems of the retina remains to be verified.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
4.
Inhibition of Na+/Ca2+ exchanger activity in cardiac and skeletal muscle sarcolemmal vesicles by monoclonal antibody 44D7 总被引:3,自引:0,他引:3
Monoclonal antibodies 44D7 and 4F2 inhibited specifically the Na+-dependent Ca2+ fluxes characteristic of the Na+/Ca2+ exchanger in cardiac and skeletal muscle sarcolemmal vesicles. Preincubation of membrane vesicles with monoclonal antibody 44D7 inhibited 90% of the Na+-dependent Ca2+ uptake measured in the first 10 s of the reaction and 50% of that measured after 60 s. Ca2+/calmodulin-dependent ATPase activity and ATP-dependent Ca2+ uptake by sarcolemmal vesicles were not affected by monoclonal antibody 44D7 whereas the Na+-dependent release of accumulated Ca2+ was inhibited. In the presence of the 44D7 antigen isolated from human kidney, monoclonal antibody 44D7 could no longer inhibit Na+-dependent Ca2+ fluxes. The distribution of 4F2 antigenic activity in the isolated muscle membrane fractions correlated with that of Na+/Ca2+ exchanger activity; cardiac and skeletal muscle sarcolemmal vesicles expressed higher levels of the antigen than skeletal muscle transverse tubule membrane, while no antigen could be detected in sarcoplasmic reticulum membranes. Our results suggest that monoclonal antibodies 44D7 and 4F2 interact either directly with the Na+/Ca2+ exchanger molecules or with some other protein(s) responsible for the regulation of this activity in the heart and skeletal muscle. 相似文献
5.
Summary In the present study we have investigated the presence and distribution of calreticulin in plant protoplasts. Calreticulin was purified from plant homogenates using a selective ammonium sulfate precipitation procedure developed for the purification of mammalian calreticulins and shown to bind calcium in45Ca2+ overlay assays. The protein was localized to plant cell endoplasmic reticulum by the indirect immunofluorescence staining of protoplasts with anti-calreticulin antibodies. No calreticulin was observed within large vacuoles. We conclude that calreticulin is present in the endoplasmic reticulum of plant cells, where, by analogy to the mammalian endoplasmic reticulum, it may play a major role in Ca2+ binding and storage.Abbreviations ER
endoplasmic reticulum
- SR
sarcoplasmic reticulum
- SDS-PAGE
sodium dodecyl sulfate-polyacrylamide gel electrophoresis
- PBS
phosphate-buffered saline 相似文献
6.
7.
The role of the primary amino groups of lysine sidechains in Ca2+ binding to calreticulin was evaluated by chemical modification of the amino group with 2,4,6-trinitrobenzenesulfonic acid (TNBS). TNBS binding to calreticulin could be described by two steps: (i) a fast reaction, with low affinity, and (ii) a slow reaction with a relatively high affinity. Inclusion of Ca2+ and/or Mg2+ decreased both the amount of TNBS bound to calreticulin and the apparent affinity constant of the slower reaction. In contrast, the properties of the faster reaction for TNBS binding were not sensitive to Ca2+ and/or Mg2+. Analysis of TNBS binding to the carboxyl-terminal (C-domain) and aminoterminal (N-domain) of calreticulin revealed that theC-domain andN-domain are responsible for the slow and fast component of the TNBS binding, respectively. In keeping with this, in the presence of Ca2+, TNBS binding to theC-domain was significantly reduced, whereas modification of theN-domain was unaffected. TNBS modification of calreticulin significantly decreased Ca2+ binding to the low affinity/high capacity Ca2+ binding site(s) which are localized to theC-domain but had no effect on the high affinity/low capacity Ca2+ binding localized to theN-domain.In theC-domain of calreticulin, which contains the low affinity/high capacity Ca2+ binding sites, acidic residues are interspersed at regular intervals with one or more positively charged lysine and arginine residues. Our results indicate that the aminogroups of the lysine sidechains in theC-domain of calreticulin have a role in the low affinity/high capacity Ca2+ binding that is characteristic of this region of the protein and which is proposed to contribute significantly to the capacity of the endoplasmic reticulum Ca2+ store. (Mol Cell Biochem130: 19–28, 1994)Abbreviations TNBS
2,4,6-Trinitrobenzenesulfonic Acid
- GST
Glutathione S-Transferase
- SDS-PAGE
Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis
- EDTA
Ethylenediaminetetraacetic Acid
- EGTA
Ethylene Glycol bis(-aminoethylether)-N,N,N,N-tetraacetic Acid
- MOPS
4-Morpholinepropanesulfonic Acid 相似文献
8.
9.
R. Gondko W. Michalak A. Rogala Dr. B. Rózga M. Adamska 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1977,51(2):87-93
Summary Leghorn, Cornish and White Rock hens were subjected to starvation. Free amino acids were determined in blood samples taken after 48, 72 and 96 h of starvation. A progressive decrease in concentration of the majority of amino acids was found. Changes in amino acid concentrations during starvation were dependent on the breed of hen. 相似文献
10.
Karol Mičieta 《Folia Geobotanica》1983,18(3):329-331