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The present study compared and examined the characteristics of actomyosin among white (W), pink (P), and red (R) muscle fiber types in carp (cultured). Both the superprecipitation reaction and the Mg2+‐ATPase activity of actomyosin became higher with increased Ca2+ concentration (pCa 7.0–pCa 5.0) and with decreased adenosine triphosphate (ATP) concentration (3.0–0.5 mM) in all three muscle fiber types. A comparison of the three fiber types shows that the superprecipitation reaction of actomysoin was lower in the order of W < P < R and, in contrast, was higher for Mg2+‐ATPase activity in the order of W > P > R. A significantly positive correlation between both values was found for each of the three muscle fiber types, but these correlations were clearly different among the three muscle fiber types, and the superprecipitation reaction of actomyosin was lower in the order of W < P < R when Mg2+‐ATPase activity was at the same level. In conclusion, the characteristics of actomyosin were remarkably different among white, pink, and red muscle fiber types.

SUMMARY : As part of a program to clarify the influence of difference of muscle fiber types in ordinary muscle on rigor mortis progress of fish, this study compared and examined the biochemical and physiological characteristics of muscle fiber types in relation to the muscular contraction and relaxation among white (W), pink (P), and red (R) muscle fibers of carp (cultured). The contents of ATP‐related compounds and glycogen just after killing, lactate dehydrogenase activity, and myofibrillar Mg2+‐ATPase activity in ordinary muscle were higher in the order of W > P > R, R ≒ P >> W, W ≒ P >> R, and P ≥ W >> R, respectively. From these results, it was suggested that the capacity of anaerobic energy supply for rigor mortis progress might be higher in the order of pink muscle fiber, white muscle fiber, and red muscle fiber. The maximum level reached by caffeine contraction was considerably higher in pink muscle fiber than in white muscle fiber, in the order of P >> W > R. However, sarcoplasmic reticulum (SR) Ca2+‐ATPase activity, SR Ca2+ uptake rate, and SR Ca2+ release rate were not higher in pink muscle fiber than in white muscle fiber, in the order of P ≒ W >> R, W > P > R, and W > P > R, respectively. The surface area and volume percentages of SR against sarcomere were higher in the order of P > W > R and P >> W > R, respectively, and well supported the result of caffeine contraction. The superprecipitation reaction of actomyosin was higher in the order of P ≥ R >> W. This result suggested that the characteristic of actomyosin in relation to muscular contraction may be markedly different among white, pink, and red muscle fibers.

SUMMARY: In order to clarify the influence of the interposition of pink muscle fiber into the dorsal ordinary muscle on the post‐mortem temporal change of K‐value, using carp, the dorsal muscle was divided into three muscle parts toward depth with the naked eye, as follows: dark muscle part, intermediate muscle part, and deepest ordinary muscle part. The muscle fiber types in these parts were discriminated by the inactivation of actomyosin ATPase activity for both acid and alkaline pre‐incubations, and the temporal changes of ATP related compounds in these parts were then measured at a kept temperature of 32°C. Three muscle parts were organized from the muscle fiber types as follows: dark muscle part was organized from only red muscle fiber type, intermediate part from only pink muscle fiber type in a thin layer and from two muscle fiber types of not only pink muscle fiber but also white muscle fiber of the IIa or IIb subtype in a region of mosaic pattern, and deepest ordinary muscle part from two muscle fiber types of white muscle fiber IIa or IIb. The temporal change of K‐value among muscle fiber types was considerably different and remarkably faster in the order of red muscle fiber, pink muscle fiber, and white muscle fiber. From these results, it was considered that the interposition of pink muscle fiber into the dorsal ordinary muscle might accelerate the temporal change of K‐value.