Hong S B, Farrand S K
Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana 61801, USA.
J Bacteriol. 1996 Apr;178(8):2427-30. doi: 10.1128/jb.178.8.2427-2430.1996.
Catabolic mannopine (MOP) cyclase encoded by certain Agrobacterium Ti and Ri plasmids lactonizes MOP to agropine (AGR). The enzyme, purified to homogeneity from a recombinant clone, has a molecular mass of 45 kDa as measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and size exclusion chromatography. The enzyme catalyzed the lactonization of MOP to AGR without the need for any cofactors. The enzyme also converted AGR to MOP with the lactonizing activity being predominant over the reverse reaction. MOP cyclase is specific for imine conjugates of D-hexose and L-glutamine and was not inhibited by sugars or amino acids. The enzyme lactonized deoxyfructosyl glutamine, a natural intermediate of MOP synthesis and catabolism, to a product indistinguishable from chrysopine, a newly discovered crown gall opine. The enzyme also lactonized N-l-(1,2-dideoxy-D-mannityl)-L-glutamine, indicating that a hydroxyl group at carbon atom 2 of the sugar moiety is not required for the enzymatic reaction.
某些根癌土壤杆菌Ti质粒和Ri质粒编码的分解代谢甘露碱（MOP）环化酶将MOP内酯化为农杆碱（AGR）。该酶从重组克隆中纯化至同质，通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳和尺寸排阻色谱法测定，其分子量为45 kDa。该酶催化MOP内酯化为AGR，无需任何辅因子。该酶还将AGR转化为MOP，内酯化活性在逆反应中占主导地位。MOP环化酶对D-己糖和L-谷氨酰胺的亚胺缀合物具有特异性，不受糖或氨基酸的抑制。该酶将脱氧果糖基谷氨酰胺（MOP合成和分解代谢的天然中间体）内酯化为一种与新发现的冠瘿碱金雀碱无法区分的产物。该酶还将N-1-（1,2-二脱氧-D-甘露糖基）-L-谷氨酰胺内酯化，表明糖部分碳原子2处的羟基不是酶促反应所必需的。
