Busch W A, Stromer M H, Goll D E, Suzuki A
J Cell Biol. 1972 Feb;52(2):367-81. doi: 10.1083/jcb.52.2.367.
Removal of rabbit psoas strips immediately after death and incubation in a saline solution containing 1 mM Ca(2+) and 5 nM Mg(2+) for 9 hr at 37 degrees C and pH 7.1 causes complete Z-line removal but has no ultrastructurally detectable effect on other parts of the myofibril. Z lines remain ultrastructurally intact if 1 mM 1,2-bis-(2-dicarboxymethylaminoethoxy)-ethane (EGTA) is substituted for 1 mM Ca(2+) and the other conditions remain unchanged. Z lines are broadened and amorphous but are still present after incubation for 9 hr at 37 degrees C if 1 mM ethylenediaminetetraacetate (EDTA) is substituted for 1 mM Ca(2+) and 5 mM Mg(2+) in the saline solution. A protein fraction that causes Z-line removal from myofibrils in the presence of Ca(2+) at pH 7.0 can be isolated by extraction of ground muscle with 4 mM EDTA at pH 7.0-7.6 followed by isoelectric precipitation and fractionation between 0 and 40% ammonium sulfate saturation. Z-line removal by this protein fraction requires Ca(2+) levels higher than 0.1 mM, but Z lines are removed without causing any other ultrastructurally detectable degradation of the myofibril. This is the first report of a protein endogenous to muscle that is able to catalyze degradation of the myofibril. The very low level of unbound Ca(2+) in muscle cells in vivo may regulate activity of this protein fraction, or alternatively, this protein fraction may be localized in lysosomes.
在兔子死后立即取出腰大肌条带，置于含有1 mM Ca(2+)和5 nM Mg(2+)的盐溶液中，于37℃、pH 7.1条件下孵育9小时，会导致Z线完全消失，但在超微结构上对肌原纤维的其他部分没有可检测到的影响。如果用1 mM 1,2 - 双（2 - 二羧甲基氨基乙氧基）乙烷（EGTA）替代1 mM Ca(2+)，其他条件不变，Z线在超微结构上仍保持完整。如果在盐溶液中用1 mM乙二胺四乙酸（EDTA）替代1 mM Ca(2+)和5 mM Mg(2+)，在37℃孵育9小时后，Z线会变宽且无定形，但仍然存在。在pH 7.0条件下，存在Ca(2+)时能从肌原纤维中去除Z线的一种蛋白质组分，可以通过用4 mM EDTA在pH 7.0 - 7.6条件下提取研磨后的肌肉，随后进行等电沉淀以及在0至40%硫酸铵饱和度之间分级分离来分离。该蛋白质组分去除Z线需要Ca(2+)水平高于0.1 mM，但去除Z线时不会导致肌原纤维在超微结构上出现任何其他可检测到的降解。这是关于肌肉内源性蛋白质能够催化肌原纤维降解的首次报道。体内肌肉细胞中未结合Ca(2+)的极低水平可能调节该蛋白质组分的活性，或者，该蛋白质组分可能定位于溶酶体中。
