MEMBRANE COARCTATION BY CALCIUM AS A REGULATOR FOR BOUND ENZYMES
MEMBRANE COARCTATION BY CALCIUM AS A REGULATOR FOR BOUND ENZYMES
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DOI：
10.1016/0005-2736(73)90389-1
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发表时间：
1973-01-01
期刊：
影响因子：
--
通讯作者：
SOVAK, M
中科院分区：
文献类型：
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作者：
HORVATH, C;SOVAK, M
由胰蛋白酶和胰凝乳蛋白酶与多羧酸聚合物的缀合物形成的球膜的酶活性随着周围溶液中Ca2+浓度的增加而降低。这种现象是可逆的，归因于膜结构的缩窄，而不是结合酶的内在行为的变化。缩窄减少了溶胀并增加了膜的虚拟交联，从而降低了底物到催化位点的扩散速率。结果，总体酶活性降低，观察到的反应偏离米氏动力学。与游离溶液中的胰蛋白酶不同，胰蛋白酶缀合物的活性随着Ca2+浓度的增加而降低，因为膜缩窄的作用掩盖了Ca2+对胰蛋白酶活性的增强。这些聚羧基膜含有约 40% 的酶蛋白，其物理和化学性质与某些细胞膜（如红细胞血影）相似。结果表明，在生命系统中也可能发生Ca2+或其他多价金属离子对结合酶膜缩窄的活性的类似间接调节。
The enzyme activity of spherical membranes formed by conjugates of trypsin and chymotrypsin with a polycarboxylic polymer decreases with increasing Ca2+concentration in the surrounding solution. This phenomenon is reversible and attributed to the coarctation of the membrane structure rather than to changes in the intrinsic behavior of the bound enzymes. Coarctation decreases the swelling and increases the virtual cross-linking of the membrane so that the diffusion rate of the substrate to the catalytic sites is reduced. As a result the overal enzymic activity decreases and the observed reaction departs from the Michaelis-Menten kinetics. The activity of the trypsin conjugate decreases with increasing Ca2+concentration unlike that of trypsin in free solution, because the effect of membrane coarctation masks the enhancement of tryptic activity by Ca2+. The physical and chemical properties of these polycarboxylic membranes, which contain about 40% enzyme protein, resemble those of some cell membranes such as erythrocyte ghosts. The results suggest that a similar indirect regulation of the activity of bound enzymesviamembrane coarctation by Ca2+or other multivalent metal ions may occur in living systems also.