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Purification of Ca 2+ ‐activated K + channel protein on calmodulin affinity columns after detergent solubilization of luminal membranes from outer renal medulla
Author(s) -
Klærke Dan A.,
Petersen Janne,
Jørgensen Peter L.
Publication year - 1987
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(87)80691-9
Subject(s) - calmodulin , egta , chemistry , vesicle , affinity chromatography , chromatography , membrane , biochemistry , chaps , protein kinase a , biophysics , calcium , phosphorylation , biology , enzyme , organic chemistry
A method is developed for purification of the protein of the Ca 2+ ‐activated K + channel from outer renal medulla of pig kidney. The response of this K + channel to physiological concentrations of Ca 2+ is important for regulation of transtubular NaCl transport. In reconstituted vesicles direct addition of calmodulin doubles Ca 2+ activation with sufficient affinity ( K0.1 nM) for chromatographic purification of the protein. For purification luminal plasma membrane vesicles are isolated on metrizamide density gradients and solubilized in CHAPS. The fraction of soluble protein retained on calmodulin‐Sepharose 4B columns in the presence of Ca 2+ and eluted by EGTA is 0.7%. The purified protein has high Ca 2+ ‐activated K + channel activity after reconstitution into phospholipid vesicles. It distributes on two bands of 51 and 36 kDa after gel electrophoresis in SDS. The 36 kDa band is rapidly cleaved by trypsin and may be involved in Ca 2+ stimulation of the channel. Phosphorylation from cAMP‐dependent protein kinase strongly stimulates Ca 2+ ‐activated K + channel activity and labels the 51 kDa band suggesting that this protein is involved in regulation of K + channel opening.