Carraway K L, Fogle D D, Chestnut R W, Huggins J W, Carraway C A
J Biol Chem. 1976 Oct 25;251(20):6173-8.
Lectin inactivation of the cell surface enzyme 5'-nucleotidase has been studied in intact 13762 mammary ascites cells, cell membrane envelopes, membrane vesicles, and solubilized membranes as a means of understanding the effects of lectins on biochemical processes and the behavior of the enzyme in the membranes. The properties of the enzyme are essentially the same in the intact cells and in membrane envelopes prepared after zinc treatment of the cells. The enzyme has a Km of 25 muM and is inhibited by concanavalin A (Con A) by an apparent noncompetitive process, which is reversed by alpha-methylmannoside. Half-maximal inhibition requires about 50 mug of Con A per mg of membrane protein. The inhibition for the intact cells and membrane envelopes does not exhibit significant cooperativity. Membrane vesicles, prepared by EDTA extraction, and solubilized membranes show differences in the behavior of the nucleotidase toward Con A even though the Km of the enzyme (25 muM) and inactivation (noncompetitive) are essentially unchanged. The Hill coefficient for the inactivation process in solubilized membranes and membrane vesicles is shifted to near 2, indicating significant cooperativity in the Con A-enzyme interaction. It is suggested that this change in cooperativity may reflect a different mode of interaction with the membrane and increased enzyme mobility, although an alteration in enzyme subunit interactions cannot be ruled out at present.
作为了解凝集素对生化过程的影响以及该酶在膜中的行为的一种手段，已对完整的13762乳腺腹水细胞、细胞膜包膜、膜囊泡和可溶性膜中细胞表面酶5'-核苷酸酶的凝集素失活进行了研究。该酶在完整细胞和经锌处理后的细胞制备的膜包膜中的性质基本相同。该酶的Km为25μM，被伴刀豆球蛋白A（Con A）通过明显的非竞争性过程抑制，α-甲基甘露糖苷可逆转这种抑制作用。半最大抑制需要每毫克膜蛋白约50μg的Con A。对完整细胞和膜包膜的抑制未表现出明显的协同性。通过EDTA提取制备的膜囊泡和可溶性膜显示，核苷酸酶对Con A的行为存在差异，尽管该酶的Km（25μM）和失活（非竞争性）基本未变。可溶性膜和膜囊泡中失活过程的希尔系数移至接近2，表明Con A与酶的相互作用存在显著协同性。有人认为，这种协同性的变化可能反映了与膜相互作用的不同模式以及酶流动性的增加，尽管目前不能排除酶亚基相互作用的改变。
