Protein Components and Ultrastructure of the Arm and Mantle Muscles of Octopus Octopus vulgaris

Protein composition and myofibrillar Ca²⁺-ATPase activity of arm and mantle muscles of the octopus Octopus vulgaris were compared. Protein compositions of both muscles were very similar to each other, though protein content was much higher in the arm than in the mantle muscle. Both muscles showed a slight but clear difference in myofibrillar Ca²⁺-ATPase activity (at pH 7.0): the optimum temperature was 40°C in the arm and 42.5°C in the mantle muscle, the specific activities at their optimum temperatures being close to each other. The pH optima of both myo-fibrils appeared at 6.0, 8.5 and 10.5. Mantle myofibril generally showed a higher activity than the arm myofibril. Transmission electron microscopy showed that both muscles were of the obliquely striated type. The cells of the mantle muscle contained many mitochondria in vascular cavities, indicating that this muscle is a highly oxidative tissue, as is the dark muscle of fish.