Explore the vast range of titles available.

:  Enzymatic and structural properties of white croaker fast skeletal muscle myosin were determined and compared with those of walleye pollack counterpart. Ca2+‐ATPase activity of white croaker myosin was decreased to approximately 70% of the original activity during 1 day of storage at 0°C and pH 7.0 in 0.5 M KCl and 0.1 mM dithiothreitol, whereas that of walleye pollack was decreased to approximately 20% under the same condition. The activation energy (Ea) for inactivation of white croaker myosin calculated by the Arrhenius plot for inactivation rate constant (KD) was 1.2‐fold higher than that of walleye pollack. While Ca2+‐ATPase showed a similar KCl‐dependency for the two species, the maximal activity was observed at pH 6.2 and 6.3 for white croaker and walleye pollack, respectively. Actin‐activated myosin Mg2+‐ATPase activity of white croaker was approximately half that of walleye pollack at 0.05 M KCl and pH 7.0, although the two myosins showed a similar affinity to F‐actin with Km of 1.7 and 1.4, respectively. Limited proteolysis with α‐chymotrypsin cleaved heat‐denatured white croaker myosin mainly at heavy meromyosin/light meromyosin (HMM/LMM) junction, whereas walleye pollack myosin was cleaved at several sites in LMM as well as at the HMM/LMM junction.

In order to elucidate the molecular mechanism of transglutaminase-mediated myosin crosslinking, a fluorescent monodansylcadaverine (MDC) was incorporated into carp Cyprinus carpio myosin and the reactive Gln residues were analyzed by cyanogen bromide cleavage. The fluorescence was predominantly detected in a 10.5 kDa BrCN fragment, assumed to be located in subfragment 2 of the myosin heavy chain. Furthermore, lysyl endopeptidase digestion of the 10.5 kDa fragment revealed that MDC was specifically incorporated into the 520th Gln residue of the subfragment 2 domain. When meat paste prepared from frozen walleye pollack (Theragra chalcogramma) surimi was incubated with MDC, the fluorescence was mostly observed in a 16 kDa BrCN fragment and also slightly detected in other three bands. By digesting the 16 kDa fragment with lysyl endopeptidase, it was elucidated that MDC was incorporated specifically into Gln-520 of myosin subfragment 2, as also detected in carp. This domain around Gln-520 is likely to be a critical region for the formation of myosin heavy chain dimers that both fish species have in common. In walleye pollack, other reactive Gln residues are presumed to exist at the C-terminus of the light meromyosin. This slight difference may have a significant effect on the capacity of myosin to form tetramers or even larger multimers.

:  In order to elucidate the mechanism of the changes in gel forming characteristics of fish meat by pH‐lowering, the gelation‐temperature curve and the gelation‐moisture content curve were examined using the acidified walleye pollack surimi or neutralized one after acidification. In the gelation‐temperature curve, the gel strength was highest at 30°C and lowest at approximately 50–60°C, irrespective of pH shifting. The gel strength at 30°C and 80°C decreased with the decrease in pH value. The neutralization of acidified surimi improved the gel strength, but it was considerably lower than the original gel strength. The gel strength at 50–60°C was not affected by pH lowering. The gel strength at 80°C could not be revived to the original by pH readjustment, either in the presence or in the absence of EDTA. These results suggest that irreversible changes of meat protein take place under the low pH, and the oxidation ability of sulfhydryl (SH) groups of protein molecule is not affected by pH‐shifting.

Tropomyosins from fish skeletal muscle show high amino acid sequence homology, although their thermal stability is clearly different among species. In order to determine the regions that are responsible for the stability of this protein, five synthetic peptides of 30mer were synthesized by Fmoc method, based on the sequence of walleye pollack Theragra chalcogramma fast skeletal muscle tropomyosin, namely, N terminal Metsup(1)-Lyssup(30), the variable region Aspsup(84)-Leusup(113), the middle region Valsup(128)-Alasup(157), the region containing the conservative Cys (Leusup(176)-Lyssup(205)), and C terminal Aspsup(255)-Ilesup(284). The thermal stability of these peptides was measured by circular dichroism and differential scanning calorimetry. The helical contents of these peptides were decreased in a temperature-dependent manner, although they showed no clear melting temperature, suggesting that the enthalpy necessary for the complete denaturation of these peptides was low. Peptides Aspsup(255)-Ilesup(284) and Aspsup(84)-Leusup(113) showed the highest and second highest alpha-helical contents, respectively, and the other peptides gave rise to lower alpha-helical contents.

:  Aspolin is a polyaspartic acid‐like protein, which is originally isolated from walleye pollack Theragra chalcogramma muscle as trimethylamine‐N‐oxide (TMAO) demethylase. Although carp Cyprinus carpio muscle contains a trace amount of the enzyme substrate, TMAO, aspolin can be extracted and purified by acid treatment, successive chromatographies and polyacrylamide gel electrophoresis, and has twice the amount of that in walleye pollack muscle. Carp aspolin showed a low enzymatic activity in the presence of Fe2+ and reductants, and its Km value (100 mM) to TMAO was extremely high. It was a thermostable protein and had an unfolded conformation. The amino acid sequence of carp aspolin 1 deduced from cDNA revealed that it contained a long Asp polymer, an uninterrupted stretch of 138 Asp residues, followed by four amino acid residues, His‐Glu‐Glu‐Leu, in C‐terminus. The chain length was shorter by 42 Asp residues than that of its walleye pollack counterpart.

This chapter contains section titled: Abstract Introduction Materials and Methods Results and Discussion

Trace elements and stable isotope ratios in otoliths have been used as proxies for the migration history of teleosts; however, their application in oceanic fishes remains limited. This study reports the first use of radiocarbons in otoliths to evaluate the horizontal migration histories of an oceanic fish species, the walleye pollock Gadus chalcogrammus. We conducted radiocarbon analyses of three stocks sourced from Hokkaido, Japan. The radiocarbon concentrations from the outermost portion of the otoliths from the Japanese Pacific, Northern Japan Sea (JS), and Southern Okhotsk Sea (OS) stocks were in general agreement with the seawater radiocarbon concentration of the sampling region, suggesting that pollock of all three stocks generally inhabited the within the sea region where each pollocks were sampled throughout their life cycle. However, the radiocarbon signals also provided some indications that some JS and OS stocks may be migrating between different sea regions. The proposed novel approach of reconstructing the individual migration history of marine fish using radiocarbon in otoliths may help examine fish migration with a higher temporal and spatial resolution that could not be achieved by trace elements and stable isotope ratios. We analyzed radiocarbon concentration in otoliths of walleye poll.

From 1982–1990 to 2006–2010 in the western part of the Bering Sea biomass of the walleye pollock Gadus chalcogrammus decreased by almost an order of magnitude, from 7.2 to 0.7 million tons. However, in the last decade (2011–2020) its biomass increased to the long-term average value (4.0 million tons). In the eastern part of the sea, the pollock biomass dynamics was of the wave-like nature with the highest value in 1982–1990 and the lowest, in 2006–2010. The food spectrum of the walleye pollock is wide and includes 16 taxonomic groups of aquatic organisms. The main part of average annual food mass consumed by pollock in the Bering Sea in 1982–2020 consisted of zooplankton (74.1%). During different study periods, annual feed consumption varied from 91.1 to 373.0 (average 239.3) million tons per year. Significant fluctuations in the volume of food consumed are mainly associated with the dynamics of the species’ biomass.

The collapse of walleye pollock catch in the Korean fishing region during the late 1980s remains unresolved despite enormous efforts to recover its stock. To investigate the future fate of walleye pollock in the western East/Japan Sea (EJS) in the late 21st century, we implemented a dynamical downscaling approach by developing high-resolution regional ocean climate models (1/20°) with the selected Coupled Model Intercomparison Project 6 (CMIP6) global climate models. We analyzed the changes in the spawning days and larval distribution of walleye pollock in the western EJS. Under the SSP5–8.5 global warming scenario, the suitable spawning period ratio of walleye pollock was drastically reduced by 76%. The severe reduction in spawning days in the western EJS was mainly attributed to ocean warming caused by a decrease in atmospheric surface cooling. Moreover, our particle tracking experiment showed substantial loss of eggsand larvae south of 38° N. Our study projected a drastic collapse of walleye pollock in the western EJS and proposed a variety of collapse patterns based on local circulation under future warming conditions. These findings can help the local fishing industry adapt and assist neighboring governments in planning future fisheries management strategies.