Schmidt J, John M
Biochim Biophys Acta. 1979 Jan 12;566(1):100-14. doi: 10.1016/0005-2744(79)90253-5.
Amylomaltase and disproportionating enzyme (D-enzyme) were purified to homogeneity from cell-free extracts of Pseudomonas stutzeri using a six-step procedure. The presence of both glycosyltransferases in the same organism has not been reported before. Molecular weight determination by gel chromatography gave a value of 74,000 for the amylomaltase and 115 000 for the D-enzyme. Two subunits of different molecular weight were found in each enzyme as proved by sodium dodecyl sulfate-gel electrophoresis. The optimum pH of amylomaltase and D-enzyme activity is 7.6--7.7. Action of both glycosyltransferases on different maltodextrins showed that amylomaltase is most active with maltotetraose, and the Km value for this substrate is 7.1 mM. D-Enzyme catalyzed glucose release from maltose (Km = 8.3 mM) at a higher rate than from maltotriose and maltotetraose. With maltotriose as initial substrate, D-enzyme forms glucose, maltopentaose, maltoheptaose, maltononaose, maltoundecaose as major products. Amylomaltase acts on maltotriose, maltotetraose, and maltopentaose to form a series of homologous 1,4-alpha-glucans. No essential chain-lengthening reaction occurred with maltohexaose.
采用六步程序从施氏假单胞菌的无细胞提取物中纯化出了淀粉麦芽糖酶和歧化酶（D-酶），使其达到了均一状态。此前尚未有报道称同一生物体中存在这两种糖基转移酶。通过凝胶色谱法测定分子量，淀粉麦芽糖酶的分子量为74,000，D-酶的分子量为115,000。十二烷基硫酸钠-凝胶电泳证明，每种酶中都发现了两个分子量不同的亚基。淀粉麦芽糖酶和D-酶活性的最适pH值为7.6 - 7.7。两种糖基转移酶对不同麦芽糊精的作用表明，淀粉麦芽糖酶对麦芽四糖的活性最高，该底物的Km值为7.1 mM。D-酶催化麦芽糖释放葡萄糖（Km = 8.3 mM）的速率高于麦芽三糖和麦芽四糖。以麦芽三糖作为初始底物时，D-酶形成的主要产物为葡萄糖、麦芽五糖、麦芽七糖、麦芽九糖、麦芽十一糖。淀粉麦芽糖酶作用于麦芽三糖、麦芽四糖和麦芽五糖，形成一系列同源的1,4-α-葡聚糖。麦芽六糖未发生本质上的链延长反应。
