Quantitative assay for CASF (Ca2+-activated sarcoplasmic factor)activity,and Effect of CASF treatment on ATPase activities of Rabbit myofibrils.

The ability of CASF (Ca2+-activated sarcoplasmic factor), a proteolytic enzyme that has recently been isolated from muscle and that removes Z-disks from myofibrils, to remove soluble material from myofibrils and to alter the Mg2+-modified ATPase activity of myofibrils was studied. A new assay involving determination of soluble material released from myofibrils was developed to measure CASF activity quantitatively. Optimum pH and optimum Ca2+ concentration for CASF activity as determined by this new assay were 7.0 and 1mM, respectively. Proteolytic activity of CASF on myofibrils was prevented completely by excess EDTA. CASF treatment of myofibrils at CASF to myofibril ratios of 1:20 by weight for 30min caused a 20_??_25% increase in Mg2+-modified ATPase activity. CASF treatment for 360min under these same conditions caused a decrease in Mg2+-modified ATPase activity at the highest ionic strengths used in this study (46.7 and 66.7mM KCI). The increase in Mg2+-modified ATPase activity may originate from CASF degradation of troponin, whereas the decrease in Mg2+-modified ATPase activity may be due to CASF destruction or release of α-actinin from myofibrils. Digestion of myofibrils by CASF causes in the myofibrils (degradation of Z-lines, increase of ATPase activity) that are very similar to the changes caused by postmortem storage.