Calcium ion activation of rabbit liver alpha 1,2-mannosidase.
Calcium ion activation of rabbit liver alpha 1,2-mannosidase.
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DOI：
10.1016/s0021-9258(19)39835-7
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发表时间：
1990-02
期刊：
影响因子：
--
通讯作者：
J. Schutzbach;W. Forsee
中科院分区：
文献类型：
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作者：
J. Schutzbach;W. Forsee
兔肝α-1，2-甘露糖苷酶是一种需要钙离子的酶，参与处理天冬酰胺连接的糖蛋白寡糖。Ca~(2+)被激活，表观活化能为1.1微米。金属离子活化剂的主要作用是影响Km，而不是Vmax。该酶的动力学机制是一种有序平衡，即钙离子必须在底物之前结合，一旦底物加入酶中，金属离子就不能释放。Co2+、Mn2+、Zn2+等其他几种二价阳离子与Ca2+竞争，对酶有抑制作用。值得注意的是，镁离子对酶活性没有影响。1-脱氧甘露糖苷和Tris抑制体内糖蛋白的加工，是与底物竞争的甘露糖苷酶的抑制剂。Ca~(2+)对酶与底物亲和力的影响可能是体内酶活性调节的决定因素。
Rabbit liver alpha 1,2-mannosidase is a calcium ion requiring enzyme involved in processing the asparagine-linked oligosaccharides of glycoproteins. Ca2+ activation occurs with an apparent Ka of 1.1 microM. The major effect of the metal ion activator is on Km rather than Vmax. The kinetic mechanism of the enzyme is that of an ordered equilibrium in which Ca2+ must bind before substrate and the metal ion cannot release once the substrate has added to the enzyme. Several other divalent cations including Co2+, Mn2+, and Zn2+ were competitive with Ca2+ and inhibited the enzyme. Significantly, Mg2+ had no effect on enzyme activity. 1-Deoxymannojirimycin and Tris, which inhibit glycoprotein processing in vivo, are inhibitors of the mannosidase competitive with substrate. The effect of Ca2+ on the affinity of the enzyme for substrate may be a determinant in regulation of enzyme activity in vivo.