[Show abstract][Hide abstract] ABSTRACT: Fish muscle is rapidly degraded during post-mortem storage, due to proteolytic enzymes acting probably both on muscle cells and connective tissue. In this work we have developed a model system which may be used to study the enzymatic degradation occurring in intact post-mortem fish muscle. Degradation of myosin heavy chain (MHC) was monitored in muscle with pH adjusted to 6.05, 6.3 and 6.9 and in the presence of the enzyme inhibitors PMSF, EDTA, phenanthroline, pepstatin A, antipain, E-64 and the cysteine proteinase activator dithiothreithol (DTT). After storage, myofibrillar proteins were isolated and MHC-specific antibodies used to study the degradation in the different samples. MHC from muscle with pH 6.05 and 6.3 was degraded, while no severe degradation was observed at pH 6.9. Introduction of enzyme inhibitors into the muscle tissue clearly showed that mainly cysteine and aspartic proteinases are responsible for the in situ MHC degradation. This is supported by the severe breakdown of MHC in the muscle samples containing DTT.
[Show abstract][Hide abstract] ABSTRACT: Soft textured Atlantic salmon is a sporadic and occasionally very severe problem for the farming and processing industries. The firm and soft fillets examined in this work differed in their gelatinase activities, cross-reactivity with anti-ubiquitin and anti-cathepsin L antibodies, as well as in the in-gel α-chymotryptic peptide maps of electrophoretically isolated myosin heavy chain (MHC) bands. The immunodetections of actin, α-actinin, MHC, and the MALDI TOF MS peptide mass fingerprinting of electrophoretically isolated MHCs only showed minor differences between samples. Other analyses revealed merely individual differences. These results seem to indicate a higher level of gelatinase activation, ubiquitination and cathepsin L cross-reacting material in softer muscle. These results would be consistent with a myopathy, but also with what could be expected in the skeletal muscle of healthy salmonid fish during a normal period of hyperplastic growth.
[Show abstract][Hide abstract] ABSTRACT: Post mortem proteolytic degradation of fish fillets leads to textural changes like muscle softening and gaping. In this study proteolytic degradation of myosin heavy chain (MHC) was monitored during storage of muscle and of isolated myofibrils at different temperatures and pH-values by the use of MHC-specific antibodies. The ability of cathepsin D to associate to myofibrillar proteins was also studied. Muscle stored at 6 °C and isolated myofibrils stored at 0 °C, 6 °C and 20 °C were degraded at pH 6.3 or lower. Cathepsin D could be found associated with extensively washed myofibrils. Inhibition of cathepsin D during storage affected the observed MHC-degradation at pH 5.5, but not at pH 6.3. This indicates that cathepsin D to a less extend than formerly believed, is responsible post mortem degradation of MHC.
[Show abstract][Hide abstract] ABSTRACT: The isolated cathepsin D-like enzyme from Atlantic cod (Gadus morhua L.) liver was shown to be a monomer with a molecular mass of approximately 40 kDa. It was inhibited by Pepstatin A and had an optimum for degradation of haemoglobin at pH 3.0. The purified enzyme had lower temperature stability than bovine cathepsin D. Antibodies raised against the purified enzyme and against two C-terminal peptides of cod cathepsin D recognized a 40 kDa protein in immunoblotting of the samples from the purification process. Both antisera showed cross reactivity with a similar sized protein in liver from cod, saithe (Pollachius virens L.), Atlantic herring (Clupea harengus L.) and Atlantic salmon (Salmo salar L.). A protein of same size was detected in wolffish (Anarhichas lupus L.) liver with the antibody directed against the purified enzyme. This antibody also recognized the native enzyme and detected the presence of cathepsin D in muscle of cod, saithe, herring and salmon. These antibodies may be useful in understanding the mechanisms of post mortem muscle degradation in fish by comparing immunohistochemical localization and enzyme activity, in particular in cod with different rate of muscle degradation. They may also be used for comparing muscle degradation in different fish species.
Comparative Biochemistry and Physiology Part B Biochemistry and Molecular Biology 08/2007; 147(3):504-11. · 2.07 Impact Factor