Isoenzymes of cAMP-dependent protein kinase in developing rat liver and in malignant hepatic tissues

Total R proteins and total cAMP-dependent protein kinase activity during rat liver development reach highest values per unit DNA when the organ has attained full metabolic competence. The parallel changes indicate coordinate synthesis of R and C subunits during hepatic development. In contrast to total R2 . C2, protein kinase activation and endogenous cAMP levels were highest around birth. Immunotitration with anti-RI and anti-RII in the presence of protein-A-Sepharose of extracts obtained from various developmental stages and from hepatomas suggested a relation of both protein kinase I and II to the terminal differentiation of the organ rather than to cellular proliferation rates. The type-II enzyme appears to be subject to additional regulations connected with neonatal adaptation phenomena. A non-enzymic analysis of the protein kinase activation status is described. It is based on the determination of the ratio of amounts: R . cAMP/total R, which showed a linear correlation with the conventional protein kinase activity ratio (-cAMP/+cAMP).