Denaturation of myosins

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).

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. 

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. 

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. 

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). 

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

Heavy Metals. Heavy metals are known to denature proteins. Acceleration of freeze denaturation of trout myosin by Cu2+ has been observed (72). In stored Gadoid muscle, Cu2+ accelerates the transformation of trimethylamine oxide to HCHO via trimethylamine and dimethylamine, in turn, and the HCHO might bind to proteins, resulting in their denaturation (106). 

The denaturation of other meat components take place at the following temperatnres althongh there are some variations from these temperatnres among breeds and muscles (Voutila et al 2007) myosin tails at 40°C-54°C, myosin heads at 53°C-60°C, collagen at 56°C-62°C, and actin at 66°C-73°C (Martens et al., 1982). 

Similar large entropy changes, suggesting important conformational changes, have been found for the denaturations of protein molecules and for the attachment of ATP to the muscle enzyme myosin. 

Fig. 18. Denaturation of L-myosin. The peak on the left in each case is L-myosin (sjj = 7.1). The right-hand peaks (b) and (c) are denatured L-myosin (sj = 12 in (b) and > 15 in (c)). (a) is once crystallized 4 days post mortem ...

Pig. 23. Sedimentation curves of L-myosin and actomyosin. Points O,pure, homogeneous L-myosin V, denatured, homogeneous L-myosin A, components from mixtures of pure and denatured L-myosin 4 homogeneous natural actomyosins -(-, natural actomyosins with two components a, actomyosin from actin and L-myosin. Curve 1 L-myosin curve la, denatured L-myosin of Sjo = 15 curves 2, 3, and 4 actomyosin. The broken curve 2 is extrapolated by means of the... 

Denaturation of L-Myosin from Sedimentation Experiments (from Portzehl et al., 1950)... 

Suiimi is a concentrate of insoluble muscle proteins (ca. 20%). It forms a solid cohesive gel with water (ca. 80%), which solidifies when warm For production, lean fish meat is ground at 5-10 °C and extracted with water until basically only myosin, actin, actomyosin and small amounts of collagen remain. The addition of paramyosin (cf. 13.1.4.2.2) intensifies the structure of the gel. In the further processing of Surimi to Kamboko, starch (ca. 5%), egg white, flavor enhancers, colorants and aroma substances are added, whereby an attempt is made to imitate crab or mussel meat. The resulting mixture is solidified by denaturation of the proteins first at 40-50 °C and then at 80-90 °C. Fibrous structures are produced by extrusion. 

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. 

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.

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). 

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). 

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