Pajares M A, Durán C, Corrales F, Mato J M
Instituto de Investigaciones Biomédicas, C.S.I.C., Madrid, Spain.
Biochem J. 1994 Nov 1;303 ( Pt 3)(Pt 3):949-55. doi: 10.1042/bj3030949.
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.
已对蛋白激酶C（PKC）磷酸化对大鼠肝脏S-腺苷甲硫氨酸合成酶（AdoMet合成酶）的调节作用进行了研究，AdoMet合成酶是甲硫氨酸代谢中的关键酶。该激酶可使该酶的四聚体和二聚体两种形式在序列的同一残基Thr-342处发生磷酸化。二聚体的磷酸化导致其解离，产生完全活性的单体。已对单体的动力学进行了研究，计算得出其甲硫氨酸的Km值为931.9微摩尔，ATP的Km值为708微摩尔，Vmax为66.8纳摩尔/分钟/毫克。用碱性磷酸酶处理两种酶形式（四聚体和二聚体）会使其活性降低，而寡聚状态不变。另一方面，用碱性磷酸酶处理后的AdoMet合成酶形式经PKC磷酸化会导致二聚体解离产生单体。再次磷酸化发生在序列的同一残基Thr-342处。文中进一步讨论了PKC磷酸化对AdoMet合成酶调节的意义。
