title: Ca 2+ -specific removal of Z lines from rabbit skeletal muscle.
abstract: 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.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002458:Cell Fractionation; D002614:Chelating Agents / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004589:Electrophoresis, Disc; D008274:Magnesium / Q000494:pharmacology*; D008854:Microscopy, Electron; D008858:Microscopy, Phase-Contrast; D009119:Muscle Contraction / Q000187:drug effects; D009124:Muscle Proteins / Q000302:isolation & purification; D009132:Muscles / Q000166:cytology* / Q000187:drug effects; D009210:Myofibrils / Q000187:drug effects*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum; D013997:Time Factors; D014020:Tissue Extracts / Q000302:isolation & purification / Q000494:pharmacology*
chemical_list: D002614:Chelating Agents; D009124:Muscle Proteins; D014020:Tissue Extracts; D004492:Edetic Acid; D008274:Magnesium; D002118:Calcium