Sola-Penna M, Vieyra A, Meyer-Fernandes J R
Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Brasil.
Z Naturforsch C J Biosci. 1994 Jan-Feb;49(1-2):141-6. doi: 10.1515/znc-1994-1-221.
Trehalose, the disaccharide of glucose, inhibits both initial rate and maximal capacity of ATP-dependent Ca2+ transport in inside-out vesicles of basolateral membrane from kidney proximal tubules. This inhibition (I0.5 = 60 mM) cannot be attributed to an increase in Ca2+ permeability, since the rate of EGTA-stimulated Ca2+ efflux from preloaded vesicles is not modified by trehalose. In the presence of 600 mM trehalose, Ca2+ uptake was almost completely inhibited, but the Ca(2+)-stimulated ATPase activity was unaffected; thus trehalose uncouples the Ca2+ transport from the ATPase activity. The Ca2+ transport inhibition by trehalose is reversible, since the inhibition disappeared when the vesicles were pre-incubated with 600 mM trehalose and then diluted in reaction medium to measure Ca2+ accumulation. Other mono- and disaccharides such as glucose, fructose, galactose, sucrose, maltose and lactose were tested but were not so effective as trehalose. The uncoupling of Ca2+ transport from hydrolysis can be explained by an interaction of trehalose with the phospholipid environment of the enzyme that induces conformational changes in specific domains of the enzyme so as to impair the coupling process.
海藻糖是葡萄糖的二糖，它能抑制肾近端小管基底外侧膜内翻小泡中ATP依赖的Ca2+转运的初始速率和最大容量。这种抑制作用（I0.5 = 60 mM）不能归因于Ca2+通透性的增加，因为海藻糖不会改变EGTA刺激的预装载小泡中Ca2+外流的速率。在600 mM海藻糖存在的情况下，Ca2+摄取几乎完全被抑制，但Ca(2+)刺激的ATP酶活性不受影响；因此，海藻糖使Ca2+转运与ATP酶活性解偶联。海藻糖对Ca2+转运的抑制作用是可逆的，因为当小泡与600 mM海藻糖预孵育，然后在反应介质中稀释以测量Ca2+积累时，抑制作用消失了。还测试了其他单糖和二糖，如葡萄糖、果糖、半乳糖、蔗糖、麦芽糖和乳糖，但它们的效果不如海藻糖。Ca2+转运与水解的解偶联可以通过海藻糖与酶的磷脂环境相互作用来解释，这种相互作用会诱导酶特定结构域的构象变化，从而损害偶联过程。
