Knowles A F
Department of Biology, Northeastern University, Boston, Massachusetts 02115.
Arch Biochem Biophys. 1988 Jun;263(2):264-71. doi: 10.1016/0003-9861(88)90635-2.
A human hepatoma cell line (Li-7A) possesses ectoATPase activity which is activated by either Mg2+ or Ca2+. Both ectoMg2+-ATPase and ectoCa2+-ATPase hydrolyze other nucleoside triphosphates, are inactive with ADP and AMP, and are inhibited by both p-chloromercuriphenyl sulfonate (pCMPS) and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. Different Km values for ATP and pH curves are obtained for ectoMg2+-ATPase and ectoCa2+-ATPase. The specific activities of the two ATPases remain relatively constant through several days of cell growth after an initial decrease. In contrast, the specific activities of the two ATPases, especially the ectoCa2+-ATPase, increases continuously in Li-7A cells cultured in the presence of EGF, cholera toxin, and hydrocortisone. The ATPases of the factor-treated cells are also indiscriminate with respect to nucleoside triphosphate substrates; however, the kinetic constants for substrates are altered when compared to that of the untreated cells. Most strikingly, the sensitivity to inhibitors is greatly reduced. It is concluded that the long-term effect of EGF, cholera toxin, and hydrocortisone on the Li-7A cells is the induction or activation of a new or minor component of the ectoATPases, which is preferentially activated by Ca2+ and insensitive to pCMPS.
一种人肝癌细胞系（Li - 7A）具有外切ATP酶活性，该活性可被Mg2+或Ca2+激活。外切Mg2+-ATP酶和外切Ca2+-ATP酶都能水解其他核苷三磷酸，对ADP和AMP无活性，且受到对氯汞苯磺酸盐（pCMPS）和4,4'-二异硫氰基芪-2,2'-二磺酸的抑制。外切Mg2+-ATP酶和外切Ca2+-ATP酶对于ATP的Km值和pH曲线不同。两种ATP酶的比活性在最初下降后，在细胞生长的几天内保持相对恒定。相比之下，在表皮生长因子（EGF）、霍乱毒素和氢化可的松存在的情况下培养的Li - 7A细胞中，两种ATP酶，尤其是外切Ca2+-ATP酶的比活性持续增加。经因子处理的细胞的ATP酶对于核苷三磷酸底物也不加区分；然而，与未处理细胞相比，底物的动力学常数发生了改变。最显著的是，对抑制剂的敏感性大大降低。结论是，EGF、霍乱毒素和氢化可的松对Li - 7A细胞的长期影响是诱导或激活了外切ATP酶的一种新的或次要成分，该成分优先被Ca2+激活且对pCMPS不敏感。
