title: Differences in thermal sensitivities of the regulatory-catalytic and catalytic forms of cyclic AMP-dependent protein kinases from various tissues.
abstract: The cAMP-dependent protein kinase from various tissues was more thermally sensitive when activated by cAMP than the non-activated enzyme. For example, when the activity ratio (the activity of protein kinase assayed -cAMP/+cAMP) was 0.40, 80% and 76% of total hepatic cAMP dependent protein kinase activity was recoverable after incubations at 45 degrees C for 15 and 30 minutes, respectively. However, when the activity ratio was elevated to about 0.80 - 0.90 by increasing cAMP levels in vivo or adding exogenous cAMP to soluble liver extracts, the total protein kinase activity recoverable after incubations at 45 degrees C for 15 minutes was 34-44% and 19-22%, respectively. This observation was used to estimate the degree of activation of the enzyme in vivo and in vitro, since the loss of enzyme activity at 45 degrees C was directly related to the degree of activation of the enzyme in tissue extracts. The regulatory-catalytic form of cAMP-dependent protein kinase was thermally resistant at 45 degrees C unless activated by incubation with exogenous cAMP, histones or NaCl, while the catalytic form of the enzyme was highly thermally sensitive at this same temperature. These data describe a new property of the cAMP-dependent protein kinase and suggest an alternative method which measure the degree of activation of the enzyme.
mesh_terms: D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002384:Catalysis; D002467:Cell Nucleus / Q000201:enzymology; D000242:Cyclic AMP / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D006358:Hot Temperature; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D009928:Organ Specificity; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats
chemical_list: D007527:Isoenzymes; D003994:Bucladesine; D000242:Cyclic AMP; D011494:Protein Kinases