Homology between regulatory subunits of type I cyclic AMP-dependent protein kinases from bovine and murine cells

The major cAMP-binding proteins isolated from ³⁵S]methionine-labeled S49 mouse lymphoma cells or MDBK bovine kidney cells correspond in isoelectric point and apparent molecular weight to the regulatory subunit (R) of type I cAMP-dependent protein kinase. These proteins were compared directly by two-dimensional gel electrophoresis and by two-dimensional gel electrophoresis of peptides generated either from native R with thermolysin and chymotrypsin or from denatured R with papain. Both the undigested proteins and all their major peptides were identical in charge and apparent molecular weights, indicating a very high degree of structural homology.