title: Developmental changes in the endogenous Ca2+-stimulated proteolysis of mouse lung cAMP-dependent protein kinases.
abstract: Regulatory subunits (R subunits) of mouse lung cAMP-dependent protein kinases undergo age-dependent changes in endogenous proteolysis, with the greatest amount of the major Mr = 37,000 proteolytic fragment detectable during fetal and neonatal development. Homogenization of lung in the presence of various protease inhibitors does not affect this age-related difference, suggesting that the observed quantitative change in R subunit proteolysis occurs in vivo. Mechanisms were sought to account for this age-dependent change. The production of a Mr = 37,000 proteolytic fragment can be stimulated in lung extracts by the addition of exogenous calcium and is due to the action of an endogenous Ca2+-stimulated protease. Neonatal lung extracts show more Ca2+-stimulated proteolysis of R subunits than adult extracts, although only slight age-related differences in either the Ca2+-stimulated protease or its specific endogenous inhibitor were observed. Age-dependent differences in R subunits which may affect sensitivity to proteases were also examined. Analysis of the two-dimensional patterns of adult and neonatal 8-N3-[32P]cAMP-labeled R subunits before or after limited proteolysis with trypsin suggests that the R subunits are structurally similar. Differences are found, however, in the relative proportions of adult and neonatal Type I R subunits (RI) in the holoenzyme or dissociated forms. An increased proportion of neonatal R subunits exist in the dissociated state, whereas adult R subunits exist primarily in the holoenzyme form. Dissociated R subunits from mouse lung are more susceptible than the holoenzyme to limited proteolysis by the partially purified lung Ca2+-stimulated protease. Dissociation of the holoenzyme in vivo may be a major factor in the age-dependent proteolytic changes observed in mouse lung protein kinases.
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives; D000345:Affinity Labels; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism; D001386:Azides; D002118:Calcium / Q000494:pharmacology*; D000242:Cyclic AMP / Q000494:pharmacology*; D005260:Female; D008168:Lung / Q000196:embryology / Q000201:enzymology / Q000254:growth & development*; D046911:Macromolecular Substances; D008297:Male; D051379:Mice; D008805:Mice, Inbred A; D010446:Peptide Fragments / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*
chemical_list: D000345:Affinity Labels; D001386:Azides; D046911:Macromolecular Substances; D010446:Peptide Fragments; D011480:Protease Inhibitors; C012760:8-azidoadenosine; D000242:Cyclic AMP; D011494:Protein Kinases; D010447:Peptide Hydrolases; D000241:Adenosine; D002118:Calcium