Journal of Biological Chemistry
There are at least three isozymes (Cα, Cβ, and Cγ) of the mammalian catalytic (C) subunit of cAMP-dependent protein kinase (PKA) (Beebe, S., Oyen, O., Sandberg, M., Froysa, A., Hansson, V., and Jahnsen, T. (1990) Mol. Endocrinol. 4, 465-475). To compare the Cγ and Cα isozymes, the respective cDNAs were expressed in permanently transformed Kin-8 PKA-deficient Y1 adrenal cells using the mouse metallothionein promoter. The recombinant C subunits were characterized as immunoreactive, zinc-inducible, cAMP-dependent kinase activities. In contrast to Cα, histone was a better substrate than Leu-Arg-Arg-Ala-Ser-Leu-Gly (Kemptide) for Cγ. Furthermore, Cγ histone kinase activity was not inhibited by the protein kinase inhibitor peptide (5- 24 amide), which has been widely used as a PKA-specific inhibitor. The major Cγ peak (type I) eluted from DEAE-Sepharose at a higher NaCl concentration (120 mM) than the Cα type I eluted (70 mM). Cγ and Cα type II eluted between 220 and 240 mM NaCl. Cγ required higher concentrations of cAMP than Cα did for dissociation from the mutant type I holoenzyme. These differences provided a basis for the separation of the mutant RI-associated isozymes on DEAE-Sepharose. Both Cα (41-42 kDa) and Cγ (39-40 kDa) were identified by a C subunit antibody after sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis. Zinc induced the PKA-mediated rounding phenotype in Cγ and Cα clones, thereby restoring the cells to the parent Y1 adrenal cell phenotype. Collectively, these data indicate that Cγ is an active PKA C subunit but suggest that Cγ and Cα have different protein and peptide recognition determinants.
Original Publication Citation
Beebe, S.J., Salomonsky, P., Jahnsen, T., & Li, Y. (1992). The Cγ subunit is a unique isozyme of the cAMP-dependent protein kinase. Journal of Biological Chemistry, 267(35), 25505-25512.
Beebe, Stephen J.; Salomonsky, Paul; Jahnsen, Tore; and Li, Yixin, "The Cγ Subunit is a Unique Isozyme of the cAMP-Dependent Protein Kinase" (1992). Bioelectrics Publications. 76.