Document Detail

Phosphorylation of muscarinic receptors: regulation by G proteins.
MedLine Citation:
PMID:  8441323     Owner:  NLM     Status:  MEDLINE    
Effects of G proteins on the phosphorylation of muscarinic receptors (mAChRs) have been examined. Cerebral but not atrial mAChRs were phosphorylated by any one of three types of protein kinase C and 4-6 mol of phosphate were incorporated per mol of mAChR, mostly in the 12-14 kDa from the carboxyterminus. Atrial mAChRs were better substrates of cAMP-dependent protein kinase than cerebral mAChRs. Phosphorylation of mAChRs by protein kinase C or cAMP-dependent protein kinase was not dependent on the presence of agonists and G proteins except that a slight inhibition by G proteins was observed probably because G proteins were also substrates of the two kinases. Agonist-dependent phosphorylation of atrial mAChRs or recombinant human mAChRs (m2 subtype) by a kinase (mAChR kinase), which is the same or very similar to beta adrenergic receptor kinase (beta ARK), was found to be regulated by the G proteins in a dual manner; stimulation by G protein beta gamma subunits and inhibition by G protein alpha beta gamma trimer. The inhibition by the G protein trimer is restored by addition of guanine nucleotides and is considered to be due to the formation of a ternary complex of agonist, mAChR and guanine nucleotide free G proteins. The stimulation by G protein beta gamma subunits was also observed for the light- or agonist-dependent phosphorylation of rhodopsin and beta AR by the mAChR kinase but not for the light-dependent phosphorylation of rhodopsin by rhodopsin kinase. The phosphorylation by beta ARK 1 was also found to be stimulated by G protein beta gamma subunits. The beta gamma subunit is considered to interact with the extra 130 amino acid residue carboxyterminal tail of beta ARK, which does not exist in rhodopsin kinase, and the interaction results in the activation of the kinase. We may assume that the G protein coupled receptor kinase is an effector of G protein beta gamma subunits and that one of the functions of beta gamma subunits is to stimulate the phosphorylation of G protein coupled receptors thereby facilitating their desensitization.
T Haga; K Haga; K Kameyama; H Nakata
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Review    
Journal Detail:
Title:  Life sciences     Volume:  52     ISSN:  0024-3205     ISO Abbreviation:  Life Sci.     Publication Date:  1993  
Date Detail:
Created Date:  1993-04-01     Completed Date:  1993-04-01     Revised Date:  2009-11-19    
Medline Journal Info:
Nlm Unique ID:  0375521     Medline TA:  Life Sci     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  421-8     Citation Subset:  IM    
Department of Biochemistry, University of Tokyo, Japan.
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MeSH Terms
Acetylcholine / metabolism
GTP-Binding Proteins / physiology*
Protein Kinase C / metabolism
Protein Kinases / metabolism
Receptors, Muscarinic / metabolism*
Rhodopsin / metabolism
Reg. No./Substance:
0/Receptors, Muscarinic; 51-84-3/Acetylcholine; 9009-81-8/Rhodopsin; EC 2.7.-/Protein Kinases; EC Kinase C; EC 3.6.1.-/GTP-Binding Proteins

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