Myosin denaturation

Angsupanich and Ledward (1998) showed that oxidative stability of lipids in Atlantic cod (Gadus morhud) muscle decreased after treatment at a pressure higher than 400 MPa dne to the release of metal ions from complexes. Of the major muscle proteins, myosin denatured at 100-200 MPa, whereas actin and most sarcoplasmic proteins denatured at 300 MPa. High-pressure treated hsh was harder, chewier, and gummier than both the raw and cooked prodncts. 

Vittayanont, M., Steffe, J.F., Flegler, S.L., and Smith, D.M. 2003. Gelation of chicken pector-alis major myosin and heat-denatured (J-lacto-globulin. J. Agric. Food Chem. 51 760-765. 

Buttkus, H. (1970). Accelerated denaturation of myosin in frozen solution. J. Food Sci. 35 558-562. 

Figure 1. Denaturation of myosins from various animals on treatment with urea solutions. [a]o, specific rotation , rabbit ox A, chicken O, cod , haddock A, lemon sole X> plaice V halibut (52).

Figure 2. Hypothetical mechanisms of aggregation of fish actomyosin during frozen storage. (A) King, 69 (B) Connell, 61 (C) Matsumoto ( proposal in the present paper). AM, actomyosin M, myosin MD1 and MDt, denatured myosin A, actin.

Jarenback and Liljemark (75,76) found similar changes in cod actomyosin solution and cod muscle during frozen storage. The denatured myosin was not extracted with salt solution. 

Connell has proposed that insolubilization of actomyosin during frozen storage of cod muscle is attributable to the denaturation of myosin rather than actin (89). During 40 weeks storage at -14°C, extractability of actomyosin and myosin decreased in parallel, while that of actin appeared to remain constant. The decrease in extractability of myosin was biphasic, while that of actomyosin followed an exponential curve. 

However, our work on in vitro frozen storage of isolated carp actomyosin showed that actin is denatured progressively with myosin as demonstrated by SDS-polyacrylamide disc gel electrophoresis (90). 

During the initial rapid stage, it appears that both myosin and actin undergo denaturation, while during the second stage, tropomyosin and troponin undergo denaturation (90). 

Subunits of myosin. Hanafusa (97.,98) found that isolated rabbit myosin and HMM underwent denaturation when cooled to temperatures ranging from -10° to -196°C followed by immediate thawing. Denaturation was measured by an increase in viscosity, change in absorbance at 278 nm and change in the optical rotatory dispersion coefficients, a0 and b0, in the Moffit-Young equation. The absolute value of b0 decreased while that of a0 increased with a decrease in the freezing temperature. 

Tropomyosin and troponin. Tropomyosin is apparently the most stable of the fish fibrillar proteins during frozen storage. It can be extracted long after actin and myosin become inextract-able however, it does denature gradually (90). 

These results led to the conclusion that denaturation and/or insolubilization of actomyosin and myosin during frozen storage is a result of aggregation caused by the progressive increase in intermolecular crosslinkages due to formation of hydrogen bonds, ionic bonds, hydrophobic bonds and disulfide bonds. 

Among the above hypotheses, effects of lipids (4-17,59-62, 69-71,155-159), formaldehyde (160-166), and gas-solid interface TMJ appear to be very important in Gadoid fishes. Denaturation of myofibrillar proteins caused by free fatty acids and/or lipid peroxides must occur during frozen storage. To prove this, Jarenback and Liljemark have shown by electron microscopy that, in muscle stored frozen with added linoleic and linolenic hydroperoxides, myosin became resistant to extraction with salt solution (168). 

Unfolding of globular proteins and subunits. Data on frozen storage of HMM, actin and sarcoplasmic enzymes have led us to propose that denaturation involves unfolding of the protein chain based on a decrease in enzymatic activity (myosin, HMM, and sarcoplasmic enzymes), polymerizing ability (actin) and filament forming properties (myosin) (82,99,113-116,122). 

Denaturation of myosin and actomyosin has so far been ascribed to intermolecular aggregation, but recent investigations have shown that intramolecular transconformation, the unfolding of the polypeptide chains, occurs in globular proteins and in subunits with globular structures. 

Kinetics of urea denaturation Urea denaturation, trsrpsin digestion of myosin —> Tyr A-spectrum... 

It is probable that Bailey s first interest in the muscle field, in which lies his greatest contribution, was aroused by the work of Astbury and Dickinson who showed that fibers of denatured myosin behaved in ways similar to keratin so far as their elastic properties were concerned and their structures were revealed by X-ray analysis. At this time the Chibnall group was much interested in the amino acid composition of proteins. The obvious similarities in fibrous behavior between keratin and myosin despite their differences in amino acid composition, particularly in cystine content, stimulated Bailey to make a comparative study of the composition of some of the then recognized muscle proteins. This was Bailey s first paper on muscle and extension of the... 

Kl. Kaldor, G., and Kuo, L., Effect of proteolytic enzymes and protein denaturing agents on normal and dystrophic myosins. Proc. Soc. Exp. Biol. Med. 127, 839-842... 

Myoglobin (ferro- and carbonyl) Myosin and denatured myosin Myosin... 

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