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A novel 13 kDa cytoplasmic soluble protein is required for the nucleotide (MgATP) modulation of the Na/Ca exchange in squid nerve fibers
Author(s) -
DiPolo Reinaldo,
Berberián Graciela,
Delgado Daniel,
Rojas Hector,
Beaugé Luis
Publication year - 1997
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/s0014-5793(96)01416-0
Subject(s) - axoplasm , squid , chemistry , cytoplasm , intracellular , biophysics , vesicle , atpase , biochemistry , stimulation , nucleotide , sodium calcium exchanger , membrane , microbiology and biotechnology , enzyme , biology , axon , neuroscience , ecology , gene
The Na/Ca exchange is a highly regulated transport mechanism in which MgATP, a powerful modulatory intracellular substrate, has important implications for its function. As occurs with some preparations, in squid axons, nucleotide regulation is lost after membrane vesicle isolation. This has been a significant obstacle in the biochemical characterization of the MgATP effect. An important clue in solving this long‐standing puzzle is presented in this work by showing that prolonged intracellular dialysis of squid axons produces a complete run down of the MgATP effect. Here we report that a soluble cytoplasmic factor isolated from fresh squid axoplasm and brain reconstitutes the MgATP stimulation of the Na‐gradient‐dependent 45 Ca uptake in squid optic nerve membrane vesicles. Partial purification of this factor uncovers the presence of a novel 13 kDa soluble cytoplasmic protein (SCPr) which, when microinjected in ATP de‐regulated dialyzed squid axons, completely restores the MgATP stimulation of Na o ‐dependent Ca efflux. We propose that in the squid preparation this SCPr constitutes the link between the nucleotide and target effector: the Na/Ca exchanger itself, or other plasma membrane structures which may secondarily interact with the exchanger.