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  Regulatory Processes on the Cytosplasmic Surface of the Na+/Ca2+ Exchanger from Lobster Exoskeletal Muscle

Eisenrauch, A., Juhaszova, M., & Blaustein, M. P. (2000). Regulatory Processes on the Cytosplasmic Surface of the Na+/Ca2+ Exchanger from Lobster Exoskeletal Muscle. Journal of Membrane Biology, 174, 225–235-225–235. doi:10.1007/s002320001047.

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 Creators:
Eisenrauch, Andreas1, Author           
Juhaszova, M.2, Author
Blaustein, Mordecai P.1, Author           
Affiliations:
1Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society, ou_2068289              
2Department of Physiology, University of Maryland School of Medicine, 655 West Baltimore Street, MD 21201, USA, ou_persistent22              

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Free keywords: Catalytic regulation; Ionic strength; a-chymotrypsin; Protection from proteolytic digestion
 Abstract: A partially purified preparation of the lobster muscle Na+/Ca2+ exchanger was reconstituted with, presumably, random orientation in liposomes. Ca2+ efflux from 45Ca-loaded vesicles was studied in exchanger molecules in which the transporter cytoplasmic surface was exposed to the extravesicular (ev) medium. Extravesicular Na+ (Naev)-dependent Ca2+ efflux depended directly upon the extravesicular Ca2+ concentration ([Ca2+]ev) with a half-maximal activation at [Ca2+] ev = 0.6 μm. This suggests that the lobster muscle exchanger is catalytically upregulated by cytoplasmic Ca2+, as in most other species. In contrast, at low [Na+]ev , the Ca ev -binding site (i.e., on the cytoplasmic surface) for Ca2+ transported via Ca2+/Ca2+ exchange was half-maximally activated by about 7.5 μm Ca2+. Mild proteolysis of the Na+/Ca2+ exchanger by α-chymotrypsin also upregulated the Naev -dependent Ca2+ efflux. Following proteolytic digestion in Ca-free medium, the exchanger was no longer regulated by nontransported ev Ca2+. Proteolytic digestion in the presence of 1.9 μm free ev Ca2+, however, induced only a 1.6-fold augmentation of Ca2+ efflux, whereas, after digestion in nominally Ca-free medium, a 2.3-fold augmentation was observed; Ca2+ also inhibited proteolytic degradation of the Na+/Ca2+ exchanger measured by immunoblotting. These data suggest that Ca2+, bound to a high affinity binding site, protects against the activation of the Na+/Ca2+ exchanger by α-chymotrypsin. Additionally, we observed a 6-fold increase in the Na+/Ca2+ exchange rate, on average, when the intra- and extravesicular salt concentrations were increased from 160 to 450 mm, suggesting that the lobster muscle exchanger is optimized for transport at the high salt concentration present in lobster body fluids.

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Language(s): eng - English
 Dates: 2000-01-131999-10-202000-04
 Publication Status: Published in print
 Pages: 11
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1007/s002320001047
PMID: 10758176
 Degree: -

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Title: Journal of Membrane Biology
  Other : J. Membr. Biol.
Source Genre: Journal
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Publ. Info: New York : Springer-Verlag New York
Pages: - Volume / Issue: 174 Sequence Number: - Start / End Page: 225–235 - 225–235 Identifier: ISSN: 0022-2631
CoNE: https://pure.mpg.de/cone/journals/resource/954925415943