豌豆叶片氨甲酰磷酸合成酶的一些调节特性。
Some regulatory properties of pea leaf carbamoyl phosphate synthetase.
作者信息
O'neal T D, Naylor A W
机构信息
Department of Botany, Duke University, Durham, North Carolina 27706.
出版信息
Plant Physiol. 1976 Jan;57(1):23-8. doi: 10.1104/pp.57.1.23.
Carbamoyl phosphate synthetase of pea shoots (Pisum sativum L.) was purified 101-fold. Its stability was greatly increased by the addition of substrates and activators. The enzyme was strongly inhibited by micromolar amounts of UMP (Ki less than 2 mum). UDP, UTP, TMP, and ADP were also inhibitory. AMP caused either slight activation (under certain conditions) or was inhibitory. Uridine nucleotides were competitive inhibitors, as was AMP, while ADP was a noncompetitive inhibitor. Enzyme activity was increased manyfold by the activator ornithine. Ornithine acted by increasing the affinity for Mg.ATP by a factor of 8 or more. Other activators were IMP, GMP, ITP, and GTP, IMP, like ornithine, increased the Michaelis constant for Mg.ATP. The activators ornithine, GMP, and IMP (but not GTP and ITP) completely reversed inhibition caused by pyrimidine nucleotides while increasing the inhibition caused by ADP and AMP.
豌豆嫩梢（Pisum sativum L.）的氨甲酰磷酸合成酶被纯化了101倍。添加底物和激活剂后，其稳定性大大提高。该酶受到微摩尔量的UMP（Ki小于2 μM）的强烈抑制。UDP、UTP、TMP和ADP也具有抑制作用。AMP在某些条件下会引起轻微激活，否则具有抑制作用。尿苷核苷酸与AMP一样是竞争性抑制剂，而ADP是非竞争性抑制剂。激活剂鸟氨酸可使酶活性增加数倍。鸟氨酸的作用是使对Mg.ATP的亲和力提高8倍或更多。其他激活剂有IMP、GMP、ITP和GTP，IMP与鸟氨酸一样，会增加Mg.ATP的米氏常数。激活剂鸟氨酸、GMP和IMP（但不是GTP和ITP）能完全逆转嘧啶核苷酸引起的抑制作用，同时增强ADP和AMP引起的抑制作用。
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