Muscle fish, ATPase activity

Fast and slow muscle fibres contain various isoforms of contractile proteins, which differ in amino acid sequence and functional characteristics. In some species, the expression of these isoforms varies with the acclimation temperature and correlates with adaptive changes in locomotory performance (Johnston, 1993). The ATPase activity of the contractile proteins of some species increases with reduced temperatures, but not if the fish are starving, so protein synthesis is evidently involved in the phenomenon. 

Savina, 1992). Moreover, as these authors and Silkina (1990) note, the white muscle of sluggish fish often exceeds that of highly active species in the characteristics described above. This thesis is supported by the data of Emeretli (1990) on LDH and ATPase activity measured in the muscles of horse-mackerel and scorpion fish (Figure 17). The creatine- and adenylate kinase reactions in the white muscle of sluggish fish appear to proceed at a greater rate than in more... 

Myosin. Rabbit muscle myosin is a long, thin molecule (VI400 X 20-50 A) with a molecular weight of 5 X 10. It is composed of two heavy chains and four light chains as demonstrated by SDS-polyacrylamide disc gel electrophoresis. On tryptic digestion, myosin is split into the subunits, H-meromyosin (HMM) and L-mero-myosin (LMM). HMM is further split into S-l and S-2 subunits. While LMM is a rod of V)0% a-helical content, the a-helical content for HMM, S-l and S-2 fragments is 46%, 33% and 87%, respectively. The ATPase activity is localized in the S-l subunit (33,34). Although fish myosins appear to have the same structural profile (10,22,35-40) and similar amino acid composition as rabbit myosin (39,41,42), fish myosin is different from rabbit myosin in physicochemical properties such as solubility, viscosity and stability (10,22,35-40). 

Actomyosin. At high salt concentrations ( . . 0.6 M KC1), actin and myosin combine to form actomyosin filaments giving a highly viscous solution. Actomyosin retains the ATPase activity of myosin and demonstrates "super-precipitation" on the addition of ATP (24,34). As expected, there are differences between actomyosins of rabbit and fish with respect to solubility (10,22,35,36), viscosity (46) and ultracentrifugal behavior (477. Since actomyosin is the most readily available form of myofibrillar proteins from fish muscle, its behavior relative to deterioration during frozen storage has been most frequently studied. 

Myosins isolated from various frozen stored fish muscles had slightly lower ATPase activity than those from fresh muscles (94, 95). A decrease in ATPase activity was found also with isolated carp myosin when stored at -20°C (82) the rate of decrease was faster than with actomyosin isolated from the same fish. As with actomyosin, the decrease in ATPase activity was preceded by a temporary rise in activity M50% the pre-freezing value). 

ATPase. Myosins isolated from various frozen-stored fish muscles exhibit specific activities for ATPase that are slightly lower than the specific activities of myosin from fresh muscles (73,74). The decline of ATPase activity also occurs with myosin isolated from carp, when storage is conducted at — 20°C (64). Like carp actomyosin, the decline is preceded by a temporary rise in activity. 

Suresh, A., Sivaramakrishna, B., Radhakrishnaiah, K 1995. Cadmium induced changes in ion levels and ATPase activities in the muscle of the fry and fingerlings of the freshwter fish, Cyplinus carpio. Chemosphere 30 (2), 367-375,... 

Figure 17 ATPase and LDH activity in scorpion fish (white boxes) and horse-mackerel (shaded) in spring (1) summer (2) and autumn (3). R, red muscle W, white muscle. (After Emeretli, 1990)...

Nambudiri, D.D. and Gopakumar, K. 1992. ATPase and lactate dehydrogenase activities in frozen stored fish muscle as indices of cold storage deterioration. Journal of Food Science 57 72-76. 

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