Characterization of a β-actinin-like protein in purified non-muscle cell membranes. Its activity on [formula omitted

Abstract

Treatment by EDTA of purified plasma membranes from MF 2S cells (a variant of the murine plasmacytoma MOPC 173) solubilized proteins and increased by a 1000-fold the sensitivity of ( Na + + K +)- ATPase to ouabain. When added back with Ca 2+ to treated plasma membranes, these EDTA-solubilized proteins restored the initial sensitivity of the enzyme to its inhibitor. We report the purification of a protein of M r 32 000, isolated from the EDTA-treated membrane supernatant. This protein was purified by a one-step procedure involving a preparative polyacrylamide gel electrophoresis without detergent. In the presence of Ca 2+ it was able to restore the original sensitivity to ouabain of ( Na + + K +)- ATPase from EDTA-treated membrane. This protein was shown to be similar to the β-actinin described by Maruyama by the following criteria: (1) molecular weight and amino acid composition; (2) cross-reactivity with their respective antisera; (3) in the presence of Ca 2+ the same quantitative biological activity on ouabain sensitivity of the ( Na + + K +)- ATPase . A possible interaction between β-actinin, calmodulin and membrane-bound ( Na + + K +)- ATPase is discussed.