The effects of Ca ions, EGTA and storage time on myofibrillar protein degradation, levels of Ca 2+-dependent proteases and cathepsins B, H, L and D of ostrich skeletal muscle

Abstract

The effect of Ca ions and ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) on myofibrillar protein degradation showed that when ostrich iliotibialis lateralis muscle was incubated with 10 mM EGTA at 2–4 °C for 24 hr, the activity of extracted cathepsin H was unchanged compared with a buffer-incubated sample. Ca ++ had no effect on extracted cathepsin H activity, while that of Ca 2+-dependent protease (CDP) decreased significantly ( p < 0.05). Ca 2+-treatment enhanced post-mortem changes observed in myofibrillar protein patterns (production of fragments around 30 K) that were not observed in EGTA-incubated myofibrils. The effect of storage time on shear force, CDP activity, cathepsin B, D, H and L activities and the SDS-PAGE pattern of myofibrils showed a time-dependent reduction in CDP activity. Of the cathepsins studied only cathepsin H showed a reduction (40%) in activity. The most prominent component appearing on storage at 2–4 °C had a M r of 27 K. The incubation of myofibrils with CDP mimicked the post-mortem changes. CDP may be responsible for some of the post-mortem changes observed, although shear force measurements suggest these changes do not lead to significant tenderisation.