Study on the aggregation mechanism of walleye pollack myosin

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Walleye pollack Theragra chalcogramma is one of the major sources for food processing industries in Japan. In the present study, the heat-induced aggregation mechanism for the walleye pollack myosin was investigated by using isolated pollack myosin, HMM, and LMM. According to the circular dichroism spectrometry and α-chymotryptic digestion of the walleye pollack LMM, the α-helices of N-terminal 2/3 and C-terminal 1/3 regions of the LMM were revealed to be reversibly and irreversibly unfolded, respectively, by the heat-treatment at 5O℃ for 5 min. The LMM region of intact pollack myosin showed similar denaturation process to the isolated LMM upon heat-treatment. Then, the changes in hydrophobicity of the myosin, HMM, and LMM during heat-treatment were investigated by means of ANS-fluorescent spectrometry. The ANS-fluorescence of myosin and HMM showed significant increase at temperatures higher than 40℃, however, that of LMM showed practically no change. This indicates that the increase in hydrophobiclty of the myosin by the heat-treatment is mainly due to the denaturation of HMM region. Concomitantly with the increase in hydrophobicity, turbidity of the myosin and HMM significantly increased, however, that of the LMM showed no increase. These results indiccate that the myosin and HMM form aggregates upon the heat-treatment, however, the LMM is incapable of aggregating upon the same treatment although some parts of the a-helices of the LMM unfolds irreversibly. On the other hand, it was found that the LMM formed coaggregates with myosin when heated at 40℃ for 10 min together with myosin, while it did not form coaggregates with the HMM. Thus, the LMM seemed to form coaggregates with the myosin through the interaction with the tail regions of myosin. Based on these results, we presented a schematic model for the pollack myosin aggregation by the heat-treatment.