Mitchell J L, Carter D D
Biochim Biophys Acta. 1977 Aug 11;483(2):425-34. doi: 10.1016/0005-2744(77)90070-5.
Two forms of ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) can be isolated from crude plasmodial homogenates of Physarum polycephalum. Both forms catalyze the stoichiometric production of putrescine and CO2 from ornithine, yet they are distinguished by (a) a large difference in their affinity for coenzyme (apparent Km values of 0.13 and 33 muM); (b) a differential stability to extended dialysis of crude homogenates at 4 degrees C; and (c) the tendency of the low affinity form to polymerize when suspended in low ionic strength borate and phosphate buffers. These forms appear to be alternate states of a basic catalytic subunit in that (a) they both demonstrate monomer and dimer molecular forms of 80 000 and 160 000 daltons, respectively, depending on the buffer content; (b) they coelute from DEAE-Cellulose ion-exchange columns; and (c) they vary in activity in approximately equivalent yet opposite directions in response to factors which alter this organism's growth or metabolism. These data suggest that ornithine decarboxylase activity may be modulated by the control of the transition of this enzyme between the active and the relatively less active form.
可从多头绒泡菌的粗制疟原虫匀浆中分离出两种形式的鸟氨酸脱羧酶（L-鸟氨酸羧基裂解酶，EC 4.1.1.17）。两种形式都催化从鸟氨酸化学计量地生成腐胺和二氧化碳，但它们的区别在于：（a）它们对辅酶的亲和力差异很大（表观Km值分别为0.13和33μM）；（b）在4℃下对粗制匀浆进行长时间透析时稳定性不同；（c）低亲和力形式悬浮于低离子强度的硼酸盐和磷酸盐缓冲液中时有聚合的倾向。这些形式似乎是一种基本催化亚基的不同状态，因为：（a）根据缓冲液成分，它们都分别表现出80 000和160 000道尔顿的单体和二聚体分子形式；（b）它们从DEAE-纤维素离子交换柱中同时洗脱；（c）响应改变该生物体生长或代谢的因素，它们的活性在大致相当但相反的方向上变化。这些数据表明，鸟氨酸脱羧酶的活性可能通过控制该酶在活性形式和相对活性较低形式之间的转变来调节。
