Characterization of the two size forms of the alpha 1 subunit of skeletal muscle L-type calcium channels.

The molecular properties of two size forms of the alpha 1 subunit of purified skeletal muscle calcium channels were analyzed. The minor, full-length, form, alpha 1(212), was found to have an apparent molecular mass of 214 kDa by Ferguson plot analysis, while the major, truncated, form, now designated alpha 1(190), had an apparent molecular mass of 193 kDa. Antibody mapping of the C-terminal region of alpha 1(190) with 10 anti-peptide antibodies placed the C terminus between residues 1685 and 1699. Three consensus sites for cAMP-dependent protein phosphorylation are present in the C-terminal region of alpha 1(212) but not in alpha 1(190), and they may be important for the regulation of the ion conductance activity of the calcium channel.