Tulsiani D R, Touster O
J Biol Chem. 1987 May 15;262(14):6506-14.
Swainsonine is a potent inhibitor of lysosomal alpha-D-mannosidase, causes the production of hybrid glycoproteins, and is reported to produce a phenocopy of hereditary alpha-mannosidosis. We now report that the effects of swainsonine administration in the rat are different in two respects from those found in other animals thus far studied. Swainsonine caused the accumulation of oligosaccharide in kidney and urine but not in liver or brain. The accumulated oligosaccharides were mainly Man(alpha 1-3)[Man(alpha 1-6)]Man(beta 1-4)GlcNAc, Man(alpha 1-3)[Man(alpha 1-6)[Man(alpha 1-3)]Man(beta 1-4) GlcNAc, and Man(alpha 1-3)[Man(alpha 1-6)]Man(alpha 1-6)[Man(alpha 1-3)]Man(beta 1-4)GlcNAc. Analogous branched Man4 and Man5 structures are found in pig and sheep tissues, but they are N, N'-diacetylchitobiose derivatives. The substrate specificities of rat kidney lysosomal and cytosolic alpha-D-mannosidases were investigated because in one type of hereditary alpha-mannosidosis, that occurring in man, the major storage products are linear rather than branched oligosaccharides. The lysosomal enzyme showed much greater activity toward linear oligosaccharides than toward the branched oligosaccharides induced in the kidney by swainsonine. On the other hand, cytosolic alpha-D-mannosidase preferred the branched oligosaccharides, a result suggesting that this mannosidase might be inhibitable by swainsonine and that the enzyme might play a normal role in glycoprotein catabolism. Swainsonine was indeed found to inhibit this enzyme at relatively high concentrations (I50 at 100 microM swainsonine), and concentrations of this magnitude were in fact found in the cytosol of kidney of swainsonine-fed rats. The kidney cytosolic alpha-D-mannosidase levels were reduced in these rats and, more important, the accumulated oligosaccharides were present mainly in the cytosol rather than in lysosomes. These results point to possible involvement of cytosolic alpha-D-mannosidase in glycoprotein degradation in the rat.
苦马豆素是溶酶体α-D-甘露糖苷酶的一种强效抑制剂，可导致杂合糖蛋白的产生，据报道会产生遗传性α-甘露糖苷贮积症的拟表型。我们现在报告，给大鼠施用苦马豆素的效果在两个方面与迄今为止所研究的其他动物不同。苦马豆素会导致肾脏和尿液中寡糖的积累，但肝脏或大脑中则不会。积累的寡糖主要是Man(α1-3)[Man(α1-6)]Man(β1-4)GlcNAc、Man(α1-3)[Man(α1-6)[Man(α1-3)]Man(β1-4)GlcNAc以及Man(α1-3)[Man(α1-6)]Man(α1-6)[Man(α1-3)]Man(β1-4)GlcNAc。在猪和羊的组织中发现了类似的分支Man4和Man5结构，但它们是N，N'-二乙酰壳二糖衍生物。对大鼠肾脏溶酶体和胞质α-D-甘露糖苷酶的底物特异性进行了研究，因为在人类发生的一种遗传性α-甘露糖苷贮积症中，主要的储存产物是线性而非分支寡糖。溶酶体酶对线性寡糖的活性比对苦马豆素在肾脏中诱导产生的分支寡糖的活性要高得多。另一方面，胞质α-D-甘露糖苷酶更喜欢分支寡糖，这一结果表明这种甘露糖苷酶可能会被苦马豆素抑制，并且该酶可能在糖蛋白分解代谢中发挥正常作用。实际上发现苦马豆素在相对较高的浓度下（100μM苦马豆素时的I50）会抑制这种酶，而在喂食苦马豆素的大鼠肾脏胞质中实际上发现了这种浓度。这些大鼠肾脏胞质中的α-D-甘露糖苷酶水平降低了，更重要的是，积累的寡糖主要存在于胞质中而非溶酶体中。这些结果表明胞质α-D-甘露糖苷酶可能参与了大鼠糖蛋白的降解。
