Srivenugopal K S, Adiga P R
J Biol Chem. 1981 Sep 25;256(18):9532-41.
The participation of a multifunctional enzyme (a single polypeptide with multiple catalytic activities (14)) has been demonstrated in the conversion of agmatine to putrescine in Lathyrus sativus seedlings. This enzyme (putrescine synthase) with inherent activities of agmatine iminohydrolase, putrescine transcarbamylase, ornithine transcarbamylase, and carbamate kinase has been purified to homogeneity and has Mr = 55,000. In the presence of inorganic phosphate, the enzyme catalyzed the stoichiometric conversion of agmatine and ornithine to putrescine and citrulline, respectively. The different activities associated with the enzyme copurified with near constancy in their specific activity. The enzyme catalyzed phosphorolysis and arsenolysis of N-carbamyl putrescine. The multifunctionality of putrescine synthase was also supported by 1) activity staining, 2) intact transfer of the ureido-14C group from labeled NJ-carbamyl putrescine to ornithine to form citrulline, and 3) the affinity of the enzyme toward structurally and functionally related affinity matrices. An agmatine cycle is proposed wherein N-carbamyl putrescine arising from the agmatine iminohydrolase reaction is converted to putrescine and citrulline, with the ureido group of N-carbamyl putrescine being transferred intact to ornithine. Preliminary results indicate that this series of reactions is also present in other plants.
已证实在山黧豆幼苗中，一种多功能酶（具有多种催化活性的单一多肽(14)）参与了胍丁胺向腐胺的转化过程。这种具有胍丁胺亚氨基水解酶、腐胺转氨甲酰酶、鸟氨酸转氨甲酰酶和氨基甲酸激酶固有活性的酶（腐胺合酶）已被纯化至同质，其相对分子质量为55,000。在无机磷酸盐存在的情况下，该酶分别催化胍丁胺和鸟氨酸按化学计量转化为腐胺和瓜氨酸。与该酶相关的不同活性在其比活性方面几乎恒定地共同纯化。该酶催化N-氨甲酰腐胺的磷酸解和砷解。腐胺合酶的多功能性还得到以下方面的支持：1) 活性染色；2) 将标记的N-氨甲酰腐胺中的脲基-14C基团完整转移至鸟氨酸以形成瓜氨酸；3) 该酶对结构和功能相关亲和基质的亲和力。提出了一个胍丁胺循环，其中胍丁胺亚氨基水解酶反应产生的N-氨甲酰腐胺转化为腐胺和瓜氨酸，N-氨甲酰腐胺的脲基完整转移至鸟氨酸。初步结果表明，这一系列反应在其他植物中也存在。
