Characterization of fast skeletal myosin from white croaker in comparison with that from walleye pollack

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 degrees 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 (E-a) for inactivation of white croaker myosin calculated by the Arrhenius plot for inactivation rate constant (K-D) 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 K-m of 1.7 and 1.4, respectively. Limited proteolysis with alpha-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.