Studies on the proteins of fish skeletal muscle. 5. Molecular weight and shape of cod fibrillar proteins

Glass transitions in frozen systems as influenced by molecular weight of food components

Freezing is a frequently used way to expand the storage life of foods with high water content. Under suitable cooling rates, frozen systems attain a condition of maximum freeze concentration, which is characterized by the glass transition temperature (T_g '), end point of freezing or onset of melting (T_m '), and concentration of solids (X_s ') in the maximum-freeze-concentrated matrix. The value of T_g ', T_m ', and X_s ' depends on the chemical composition of frozen system. Below T_g ', the rates of deteriorative reactions are significantly reduced. In this article, the data for T_g ', T_m ', and X_s ' of different frozen systems including sugars, starches, proteins, and food are collected and compiled. The trends in T_g ' and T_m ' data of food are investigated using molecular weight (MW) of food components. The T_g ' and T_m ' of most starches (increased by 2.46% to 87.3% and 10.8% to 85.0%) and some protein-rich foods (increased by 5.00% to 53.4% and 25.0% to 52.9%) were higher than the maximum values of sugar-rich foods. Both T_g ' and T_m ' values increased with increasing MW of solids in frozen food, reaching an asymptotic value. Moreover, there were exponential relationships between T_g ' or T_m ' values and MW for sugar and starch-rich foods taken together. Some studies found that frozen storage below T_g ' maintains the higher quality of food that was achieved by fast freezing. However, other studies found that there was no significant difference in the quality of frozen foods between storage temperature below and above T_g '. Therefore, storage below T_g ' is not the only factor for predicting the stability of frozen foods.

Comparative study of myosins present in the lateral muscle of some fish: species variations in myosin isoforms and their distribution in red, pink and white muscle

Myosin isoforms and their distribution in the various fibre types of the lateral muscle of eight teleost fish (representing a wide range of taxonomic groups and lifestyles) were investigated electrophoretically, histochemically and immunohistochemically. Polyclonal antisera were raised against slow (red muscle) and fast (white muscle) myosins of the mullet, and used to stain sections of lateral muscle. Antisera specific for fast and slow myosin heavy chains only (anti-FHC and anti-SHC respectively) and for whole fast and slow myosins (anti-F and anti-S respectively) were obtained, and their specificity was confirmed by immunoblotting against electrophoretically separated myofibrillar proteins. The ATPase activity of myosin isoforms was examined histochemically using methods to demonstrate their acid- and alkali-lability and their Ca-Mg dependent actomyosin ATPase. As expected, the predominant myosin (and fibre) type in the red muscle showed an alkali-labile ATPase activity, reacted with the anti-S and anti-SHC sera (but not anti-F or anti-FHC) and contained two 'slow' light chains, whereas the predominant myosin (and fibre) type in the white muscle showed an alkali-stable ATPase activity, reacted with anti-F and anti-FHC sera (but not anti-S or anti-SHC) and contained three 'fast' light chains. However, superimposed upon this basic pattern were a number of variations, many of them species-related. On analysis by two-dimensional gel electrophoresis fish myosin light chains LC1s, LC2s and LC2f migrated like the corresponding light chains of mammalian myosins, but fish LC1f consistently had a more acidic pI value than mammalian LC1f. Fish LC3f varied markedly in Mr in a species-related manner: in some fish (e.g. eel and mullet) the Mr value of LC3f was less than that for the other two light chains (as in mammalian myosin), whereas in others it was similar to that of LC2f (e.g. cat-fish) or even greater (e.g. goldfish). Species differences were also seen in the relative intensity of LC1f and LC3f spots given by the fish fast myosins. In most of the fish examined the red muscle layer showed some micro-heterogeneity, containing (in addition to the typical slow fibres) small numbers of fibres with a histo- and immunohistochemical profile typical of white muscle (fast) fibres. However, other immunohistochemically distinct minority fibres were found in the red muscle of the goldfish. Three types of pink muscle were distinguished: a mosaic of immunohistochemically typical red and white fibres (e.g. grey mullet).(ABSTRACT TRUNCATED AT 400 WORDS)

Studies on proteinases from the digestive organs of sardine. I. Purification and characterization of three alkaline proteinases from the pyloric caeca

Three alkaline proteinases designated I, II and III are found in the pyloric caeca of sardine and isolated by (NH4)2SO4 fractionation, DEAE-cellulose chromatography and gel filtration on Sephadex G-100. The final preparations were judged homogeneous by multiple criteria. The molecular weights of the enzymes I, II and III were determined by the sedimentation equilibrium method to be 22 900, 28 700 and 27 000, respectively. The isoelectric points were 5.45, 5.30 and 4.85, and the sedimentation coefficients (S0 20, w) were 2.91, 3.06 and 2.94, respectively. Enzymes II and III had similar amino acid compositions which were different from that of enzyme I, especially in the content of lysine, valine and tyrosine. All the enzymes belonged to a group of serine proteases. Enzymes II and III were found to be an anionic alpha-chymotrypsin-like enzymme and an anionic trypsin-like enzyme, respectively. Although these fish enzymes had properties in common with those of bovine pancreatic cationic trypsin and chymotrypsin, they are distinctly different in their optimum pH, pH stability, net charge and immunological properties.

Hydrodynamic studies on the self association of vertebrate skeletal muscle myosin

Sedimentation velocity studies on myosin A solutions at high ionic strength combined with computer-simulation of the concentration dependence of the sedimentation coefficient for a rapidly reversible monomer-dimer equilibrium have confirmed that if such an equilibrium does exist it has an equilibrium constant of less than 10 ml/g. A new hydrodynamic treatment has been used to calculate the molecular weight of myosin from s0 and ks alone and has yielded a value of 470 000. Combination of viscosity and sedimentation velocity results has shown that the myosin molecule displays little swelling (Vs/v = 1.1 +/- 0.1). A new picture of the myosin molecule is presented in which a conformational change in the head region is suggested to account for the variation in published s 0 values.

PROTEINS IN FISH MUSCLE: 16. ADENOSINETRIPHOSPHATASE ACTIVITY OF COD MYOSIN AND ACTOMYOSIN

The adenosinetriphosphatase (ATPase) activities of actomyosin extracts of prerigor and postrigor cod muscle, and of myosins prepared from them by ultracentrifugation in the presence of ATP, have been measured at ionic concentration 0.1 and pH 7.3. The actomyosin ATPases were strongly activated by Mg++, while those of the myosins were suppressed by Mg++, in agreement with corresponding rabbit skeletal muscle proteins. Ca++ ion also moderately activated the actomyosin ATPases, but had little effect on the myosin ATPases. When actomyosin was precipitated by dilution in the presence of ATP and Mg++, the characteristic activation by Mg++ was lost. The myosin ATPases were very labile.