Metabolism of exogenous cholesterol by rat adrenal mitochondria is stimulated equally by physiological levels of free Ca2+ and by GTP.
Metabolism of exogenous cholesterol by rat adrenal mitochondria is stimulated equally by physiological levels of free Ca2+ and by GTP.
复制标题
生理水平的游离 Ca2 和 GTP 同等地刺激大鼠肾上腺线粒体对外源胆固醇的代谢。
DOI：
10.1016/0303-7207(94)03441-u
复制
发表时间：
1995
影响因子：
4.1
通讯作者：
Jefcoate,CR
中科院分区：
文献类型：
--
作者：
Kowluru,R;Yamazaki,T;McNamara,BC;Jefcoate,CR
肾上腺线粒体在细胞膜细胞色素P450scc上代谢胆固醇。外源性和外膜（OM）胆固醇代谢较慢，因为胆固醇从OM到IM的转移有限。体内ACTH处理可刺激这一过程，而环己亚胺（CX）诱导的不稳定调节蛋白耗竭可抑制这一过程。在离体大鼠肾上腺线粒体中，GTP增强了外源性胆固醇的代谢，与增强膜间胆固醇转移一致（Xu et al. (1989) J. Biol Chem. 264, 17674），但容易穿过线粒体膜的20α-羟基胆固醇的代谢不受影响。不可水解的类似物GTPγ s完全抑制GTP对胆固醇代谢的激活，表明GTP需要水解。低浓度的Ca2+(0.4-4 μM)刺激两个独立的胆固醇转运过程。对于外源性胆固醇，Ca2+介导的过程可以取代GTP，因为每一个产生相当的刺激和组合产生很少的额外活性。这种Ca2+刺激对GTPγS和钌红（RR）不敏感，这阻止了Ca2+进入基质。Ca2+还增强内源性OM胆固醇对p450scc的可用性，内源性OM胆固醇在体内cx抑制期间积累。然而，这种刺激的特点是对GTP不敏感，并被RR完全抑制。因此，Ca2+增强了外源性胆固醇从OM的膜间转移，而不通过GTP独立刺激的过程进入基质。Ca2+通过完全不同的机制诱导内源性OM胆固醇的转移，包括rr抑制的基质变化。体内产生的内源性OM胆固醇无法接受gtp敏感刺激，因此其分布与体外从外源性胆固醇进入OM的胆固醇不同。体内ACTH治疗20分钟可刺激外源性胆固醇代谢2- 3倍。Ca - GTP刺激减少了这些差异，表明体外对体内激活的部分补偿。
Adrenal mitochondria metabolize cholesterol at inner membrane (IM) cytochrome P450scc. Exogenous and outer membrane (OM) cholesterol are metabolized more slowly due to a limiting transfer of cholesterol from OM to IM. This process is stimulated by in vivo ACTH treatment and inhibited by cycloheximide (CX)-induced depletion of labile regulatory proteins. In isolated rat adrenal mitochondria, GTP enhances the metabolism of exogenous cholesterol, consistent with enhanced intermembrane cholesterol transfer (Xu et al. (1989) J. Biol Chem. 264, 17674), but metabolism of 20α-hydroxycholesterol, which readily traverses mitochondrial membranes, is not affected. The non-hydrolyzable analog, GTPγS, completely inhibits the activation of cholesterol metabolism by GTP, suggesting a requirement for GTP hydrolysis. Low concentrations of Ca2+(0.4–4 μM) stimulate two independent cholesterol transport processes. For exogenous cholesterol, a Ca2+-mediated process can replace GTP since each produces comparable stimulation and the combination produces little additional activity. This Ca2+stimulation is insensitive to GTPγS and also to Ruthenium Red (RR), which prevents Ca2+entry into the matrix. Ca2+also enhances availability to P450sccof endogenous OM cholesterol, which accumulates during in vivo CX-inhibition. This stimulation is, however, distinguished by insensitivity to GTP and complete inhibition by RR. Ca2+, therefore, enhances intermembrane transfer of exogenous cholesterol from OM without entry into the matrix through a process which is independently stimulated by GTP. Ca2+induces transfer of endogenous OM cholesterol through a completely different mechanism involving RR-inhibited matrix changes. This in vivo generated endogenous OM cholesterol is inaccessible to GTP-sensitive stimulation and is therefore distributed differently than cholesterol entering the OM from exogenous cholesterol in vitro. Metabolism of exogenous cholesterol was stimulated 2- to 3-fold by a 20-min in vivo ACTH treatment. Ca GTP stimulation diminishes these differences, suggesting partial compensation in vitro for the in vivo activation.