Effect of Ca2+ on Protein Kinase A-Mediated Phosphorylation of a Specific Serine Residue in an Expressed Peptide Containing the Ca2+-Regulatory Domain of Scallop Muscle Na+/Ca2+ Exchanger

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Abstract

ABSTRACT

Sequencing of the scallop muscle Na+/Ca2+ exchanger revealed three consensus sequences for phosphorylation by PK-A in the large cytoplasmic loop (R363KLTG, R379RASV, and R618RGSV). Site-directed mutagenesis of the expressed Glu384-Ser713 segment of the f loop identified Ser621 as a residue phosphorylated by PK-A. The R618RGSV sequence is located at the junction of the mutually exclusive exon and exon 9, a site where many alternatively spliced variants of vertebrate NCX1 and NCX3 are generated. Phosphorylation of Ser621 by PK-A in the isolated Glu384-Ser713 peptide was blocked under conditions where Ca2+ was bound.

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