Beirăo P S, De Meis L
Biochim Biophys Acta. 1976 May 21;433(3):520-30. doi: 10.1016/0005-2736(76)90278-9.
(1) Ca2+ efflux from rabbit skeletal muscle sarcoplasmic reticulum vesicles pre-loaded with 45Ca2+ was studied in the presence and in the absence of external Ca2+. (2) In the absence of Ca2+ in the assay media, ADP activates the Ca2+ efflux. The increment of Ca2+ efflux requires Pi, is coupled to ATP synthesis, and is inhibited by external Ca2+ (Ki 0.1-0.2 muM). (3) When Ca2+ is added to the assay media, ADP alone activates the Ca2+ efflux, but this is coupled to a Ca2+ influx of the same magnitude. It is therefore an exchange of internal for external Ca2+ in a 1:1 ratio. (4) The ADP-activated Ca2+ exchange requires external Ca2+ with an apparent Km of 0.1-0.2 muM, does not require the addition of Pi or Mg2+, although 3-10 mM MgCl2 activates it. It is not inhibited by the removal of contaminating ATP with hexokinase plus glucose. (5) It seems likely that Ca2+ can be translocated across sarcoplasmic reticulum membrane without the formation of a phosphorylated intermediate.
（1）在有和没有细胞外钙离子的情况下，研究了预先加载45Ca2+的兔骨骼肌肌浆网囊泡中的Ca2+流出情况。（2）在测定介质中没有Ca2+时，ADP激活Ca2+流出。Ca2+流出的增加需要无机磷酸（Pi），与ATP合成偶联，并被细胞外Ca2+抑制（抑制常数Ki为0.1 - 0.2微摩尔）。（3）当向测定介质中添加Ca2+时，单独的ADP激活Ca2+流出，但这与相同量的Ca2+流入偶联。因此，这是内部Ca2+与外部Ca2+以1:1的比例进行交换。（4）ADP激活的Ca2+交换需要细胞外Ca2+，其表观米氏常数（Km）为0.1 - 0.2微摩尔，不需要添加Pi或Mg2+，尽管3 - 10毫摩尔的MgCl2可激活它。用己糖激酶加葡萄糖去除污染的ATP不会抑制它。（5）Ca2+似乎有可能在不形成磷酸化中间体的情况下跨肌浆网膜转运。
