Reiss U, Sacktor B
Biochim Biophys Acta. 1982 Jun 24;704(3):422-6. doi: 10.1016/0167-4838(82)90063-2.
The specific activities of membrane-bound maltase (alpha-d-glucoside glucohydrolase, EC 3.2.1.20) in renal cortex homogenates and isolated brush border membranes of senescent rats decreased about 30% compared to the specific activities of the enzyme from young adult animals. The decline was gradual and concomitant with the aging process. When the enzymes from rats of 25 and 6 months of age were solubilized and purified to homogeneity the same decrement with age was found, 32.5 and 46.1 units/mg of protein, respectively. This finding suggests that the decrease in maltase activity with age results from an alteration in the enzyme per se, rather than from a change in the enzyme's membrane environment, which was reflected secondarily as a loss in activity. Recoveries of enzyme activity and protein and fold-purification were similar for young and old maltase, indicating that the age-related difference in specific activities of the pure enzymes was not due to the selective purification of an altered species of enzyme. The age-associated difference in activity was not attributable to the presence of proteolytic activity in the homogenate nor to the presence of an activator in the young or an inhibitor in the old kidney. The pure enzymes from young adult and aged animals did not differ in molecular weight, electrophoretic mobility, amino acid composition and Km value. Circular dichroism spectra revealed that both the young and old enzymes contained beta-structure. However, the old enzyme had more helical structure than did the young enzyme, suggesting a conformational alteration with age.
与年轻成年动物肾脏皮质匀浆和分离的刷状缘膜中膜结合麦芽糖酶（α-D-葡萄糖苷葡萄糖水解酶，EC 3.2.1.20）的比活性相比，衰老大鼠的该酶比活性降低了约30%。这种下降是渐进的，且与衰老过程相伴。当将25月龄和6月龄大鼠的该酶溶解并纯化至均一状态时，发现随着年龄增长出现相同程度的下降，分别为32.5和46.1单位/毫克蛋白质。这一发现表明，麦芽糖酶活性随年龄下降是由于酶本身的改变，而非酶的膜环境变化，后者只是活性丧失的次要反映。年轻和老年麦芽糖酶的酶活性、蛋白质回收率以及纯化倍数相似，这表明纯酶比活性的年龄相关差异并非由于对一种改变的酶进行选择性纯化所致。活性的年龄相关差异既不归因于匀浆中蛋白水解活性的存在，也不归因于年轻肾脏中激活剂或老年肾脏中抑制剂的存在。年轻成年动物和老年动物的纯酶在分子量、电泳迁移率、氨基酸组成和Km值方面并无差异。圆二色光谱显示，年轻和老年酶均含有β结构。然而，老年酶比年轻酶具有更多的螺旋结构，这表明其构象随年龄发生了改变。
