Protein kinase C phosphorylation of rat liver S-adenosylmethionine synthetase: dissociation and production of an active monomer.
The regulation of rat liver S-adenosylmethionine synthetase (AdoMet synthetase), a key enzyme in methionine metabolism, by protein kinase C (PKC) phosphorylation has been studied. Both enzyme forms, tetramer and dimer, are phosphorylated by this kinase in the same residue, Thr-342, of the sequence. Phosphorylation of the dimer leads to its dissociation, with production of a fully-active monomer. The kinetics of the monomer have been studied, and a KmMet of 931.9 microM, a KmATP of 708 microM and a Vmax of 66.8 nmol/min/mg have been calculated. Alkaline phosphatase treatment of both enzyme forms (tetramer and dimer) produces a reduction in their activity with no change in the oligomeric state. On the other hand, PKC phosphorylation of the alkaline phosphatase-treated AdoMet synthetase forms leads to the dissociation of the dimer to produce a monomer. Rephosphorylation occurs again in the same residue, Thr-342, of the sequence. The significance of AdoMet synthetase regulation by PKC phosphorylation is further discussed.
Instituto de Investigaciones Biomédicas, C.S.I.C., Madrid, Spain.
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Pajares
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Durán
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Corrales
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Mato
D000595:Amino Acid Sequence; D000818:Animals; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D008716:Methionine Adenosyltransferase / Q000378:metabolism*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D008716:Methionine Adenosyltransferase; D011493:Protein Kinase C