title: The cyclic nucleotide-dependent phosphorylation of aortic smooth muscle membrane proteins.
abstract: Membrane proteins of Mr 240,000, 130,000, and 85,000 (GS-proteins) were rapidly and selectively phosphorylated in particulate fractions of rabbit aortic smooth muscle in the presence of [Mg-32P]ATP and low concentrations of cGMP (Ka = 0.01 microM) or cAMP (Ka = 0.2 microM). The effects of both cyclic nucleotides in this preparation were mediated entirely by an endogenous, membrane-bound form of cGMP-dependent protein kinase (G-kinase). The GS-proteins were also phosphorylated by the soluble form of G-kinase purified from bovine lung; this effect was most evident following removal of endogenous G-kinase from the membranes using Na2CO3 and high salt washes. The membrane-bound and cytosolic forms of G-kinase phosphorylated the Mr 130,000 GS-protein with the same specificity as determined by two-dimensional peptide mapping. Despite this functional homology between the two forms of G-kinase, only the particulate enzyme appears to play a role in phosphorylating the GS-proteins. Although little endogenous cAMP-dependent protein kinase (A-kinase) activity was detected in washed aortic smooth muscle membranes, the GS-proteins could be phosphorylated when purified A-kinase catalytic subunit was added to this preparation. Peptide mapping of the Mr 130,000 GS-protein indicated that A-kinase phosphorylated a subset of the same peptides labeled by the two forms of G-kinase. The endogenous A-kinase of rabbit aortic smooth muscle homogenates was also found to phosphorylate the GS-proteins. Since the intracellular concentrations of cGMP or cAMP can be selectively elevated by different stimuli, these results suggest several possible mechanisms by which the phosphorylation state of the GS-proteins may be regulated by cyclic nucleotides: activation of the membrane-bound G-kinase by cGMP or cAMP; and activation of cytosolic A-kinase by cAMP.
mesh_terms: D000818:Animals; D001011:Aorta / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology*; D006152:Cyclic GMP / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D008970:Molecular Weight; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D011817:Rabbits
chemical_list: D008565:Membrane Proteins; D000242:Cyclic AMP; D011494:Protein Kinases; D006152:Cyclic GMP