CHANGE OF REGULATORY ACTIVITY OF TROPOMYOSIN AND TROPONIN ON ACTO‐HEAVY‐MEROMYOSIN ATPase DURING POSTMORTEM STORAGE OF MUSCLE

Abstract

ABSTRACTThe effect of regulatory proteins on the actin‐myosin interaction during postmortem storage of muscle was investigated by using a reconstituted complex of actin, heavy‐meromyosin (HMM), tropo‐myosin and troponin. In the absence of calcium ions, the acto‐HMM ATPase activity was maximally inhibited by tropomyosin and troponin, from both at‐death and 168 hr postmortem muscles, at a molar ratio of tropomyosin and troponin to actin of more than 0.2. In addition, there was no apparent difference in the molar ratio required for inhibiting the ATPase activity between the regulatory proteins from at‐death and 168 hr postmortem muscles. The pCa‐dependent ATPase activity of the reconstituted complex prepared from 168 hr postmortem muscle (168 hr acto‐HMM and 168 hr tropomyosin and troponin) was higher than that of at‐death muscle (0 hr acto‐HMM and 0 hr tropomyosin and troponin) and consequently the curve was shifted toward lower calcium ions concentrations. However, little difference was found in Ca++‐sensitivity of the regulatory proteins between at‐death and 168 hr postmortem muscles. SDS‐polyacrylamide gel electrophoretograms showed that there was a slight change of myosin structure and a noticeable degradation of troponin from 168 hr postmortem muscle compared to at‐death muscle. These results suggest the possibility that the increase in myofibrillar ATPase activity during postmortem storage of muscle is mainly due to the increase in the actin‐myosin interaction.