Formation of Myofibrillar Fragments and Reversible Contraction of Sarcomeres in Chicken Pectoral Muscle

SUMMARY— As morphological changes occurred in the pectoral muscles of chicken carcasses during 48 hr storage at 5°C, two notable phenomena were observed: (1) fragmentation of myofibrils and (2) reversible or irreversible contraction of sarcomeres. When blendorized, myofibrils tend to break into small fragments composed of 1-4 sarcomeres with time post-mortem. It was also found that besides an irreversible post-mortem contraction of sarcomeres generally accepted, a reversible contraction can take place under particular conditions.     

Effect of Electrical Stimulation on Postmortem Property Change of Myofibrillar Proteins

Changes in biochemical properties of myofibrillar proteins of rabbit muscle, which had been subjected to electrical stimulation soon after slaughter, during postmortem storage at 0°C were investigated. Myofibrillar ATPase activity and the ATPase activity of acto-heavy meromyosin (HMM) complex, reconstituted from actin and HMM which had been prepared from at-death and postmortem muscles, decreased at first and then increased slightly during 7 days storage. In addition, the change of the dissociation constant of acto-HMM complex of electrically stimulated muscle during postmortem storage was quite small, i.e., 1.59 ± 10^?4M for at-death muscle, 1.70 ± 10^?4M for muscle stored for 1 day and 1.49 ± 10^?4M for muscle stored for 7 days. This indicates that electrical stimulation treatment minimized the postmortem change of actin-myosin interaction.     

Studies on Bovine Natural Actomyosin 2. Physico-Chemical Properties and Tenderness of Muscle

SUMMARY: Studies were made of physicochemical characteristics of natural actomyosin from bovine longissimus of different post-mortem ages and tenderness classifications. Reduced viscosity, ATP sensitivity, and "actin" content (polyethylene sulfonate treatment) were higher for natural actomyosin prepared from muscle 12-24 hr post-mortem than from pre-rigor muscle, which confirms previous reports for rabbit natural actomyosin. A higher actin to myosin ratio in actomyosin from muscle 12-24 hr was therefore postulated. A stronger interaction of actin and myosin in actomyosin from muscle 12-24 hr post-mortem than from pre-rigor or aged muscle was also suggested by reduced viscosity and ultracentrifugation data. Reduced viscosity differences between actomyosins from tough and tender muscle suggested a higher gel character in actomyosin from tough muscle. This possibly indicated a higher content of α-actinin. No consistent differences in ATP sensitivity, myosin and actin content of natural actomyosin of tough and tender muscle were found. Natural actomyosin from muscle aged post-mortem showed the appearance during analytical ultracentrifugation of an additional component which sedimented at about 11S to 12S. This component appeared in the actomyosin prepared from tender muscle after 24 hr but did not appear until 10 days in the actomyosin from tough muscle.     

SOME PROPERTIES OF MYOFIBRILLAR PROTEINS OBTAINED FROM LOW IONIC STRENGTH EXTRACTS OF WASHED MYOFIBRILS FROM PRE- AND POST-RIGOR CHICKEN PECTORAL MUSCLE

SUMMARY— Changes in extractability of the proteins associated with the fragmentation phenomenon of myofibrils in chicken pectoral muscle were studied. The results indicate that the protein fractions extracted by neutralized water from muscle residue. from which water-soluble proteins have been washed out, increase in post-rigor muscle. The extracts from pre- and post-rigor muscle were fractionated with ammonium sulfate into two fractions: the fraction precipitated by 1.7 M ammonium sulfate (Fr.1) and the supernatant (Fr. 2). Depressing effect on the onset of ATP-induced superprecipitation of trypsin-treated myosin 6 which was initially present in Fr. 2 from pre-rigor muscle decreased to a great extent in that from post-rigor muscle, whereas promotive effect on gelation of F-actin and superprecipitation of the myosin 6 which was little in Fr. 1 from pre-rigor muscle appeared in that from post-rigor muscle. It is proposed that an increasing amount of protein which indicates α-actinin activity is released along with the destruction and final dissolution of the Z-line structure during postmortem storage of chicken pectoral muscle.