title: Rat adipose tissue cAMP-dependent protein kinase: a unique form of type II.
abstract: The rat adipose tissue cAMP-dependent protein kinase type II holoenzyme and regulatory (R) subunit were compared with type II from bovine heart and several other species and tissues. Adipose tissue type II was similar to the bovine heart type II by several criteria (S 20,W = 7.0, site 1 and site 2 dissociation rates for [3H]cAMP, rapid autophosphorylation and lack of MgATP inhibition of [3H]cAMP binding). However, some of its physical characteristics were similar to type I. The apparent molecular weight determined by SDS gel electrophoresis of the homogeneous adipose tissue R subunit was 51000 daltons compared to 49000 for type I and 53000-58000 for other type II R subunits. The adipose tissue holoenzyme eluted from DEAE-cellulose at an intermediate position between type I and bovine heart type II. The adipose tissue and bovine heart holoenzymes differed in several properties including Stokes radius (5.2 nm vs. 6.0 nm), calculated molecular weight (157000 vs. 181000 daltons) and frictional ratio (1.47 vs. 1.60). After autophosphorylation the adipose tissue R subunit, like type IIB forms from other species and tissues, did not shift to a higher apparent molecular weight on SDS gel electrophoresis like bovine heart type IIR subunit (a type IIA form). Even though the adipose tissue enzyme was quite similar to other type II forms in the kinetics of cAMP action, the cAMP binding sites could be shown to be different from them by the use of cAMP analogs. cAMP analogs modified at the N6 position of the adenine ring, such as N6-benzoyl-cAMP, had higher apparent Ka values for protein kinase activation for the adipose tissue enzyme than for the bovine and several other heart isozymes. cAMP analogs modified at the 8 carbon of the adenine ring showed positive cooperativity of activation for the adipose tissue enzyme but not for the bovine heart holoenzyme. The adipose tissue isozyme is the first type II form described to have a distinct kinetic characteristic.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000273:Adipose Tissue / Q000201:enzymology*; D000818:Animals; D002417:Cattle; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism; D007527:Isoenzymes / Q000302:isolation & purification* / Q000378:metabolism; D007700:Kinetics; D008970:Molecular Weight; D009206:Myocardium / Q000201:enzymology; D011487:Protein Conformation; D011494:Protein Kinases / Q000302:isolation & purification* / Q000378:metabolism; D051381:Rats
chemical_list: D007527:Isoenzymes; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D011494:Protein Kinases