An amount of water held by the isolated myofibrils from carp dorsal muscle was measured using a modification of the centrifugation technique. A specific amount of water retained was determined from the apparent specific amount of water retained in the myofibrils by subtracting the amount of interstitial water remaining in the wholly denatured myofibrils. It was thus found that the specific amount of water held in myofibrils was minimal at a NaCI concentration range of 0.01-0.2M. The myosin B suspension retained 4 times the amount of water than that of the myofibrils.
At a final concentration of Tris-acetate buffer (pH7.0) between 2.5-20mM, the specific amount of water held by the myofibrils was found to be inversely proportionate to the concentration of the buffer. Therefore, we proposed that a product of the specific amount of water and the buffer concentration is an useful index for assaying the water holding capacity of the myofibrils. Using this index, it was shown that the water holding capacity of the myofibrils decreased in accordance with the first order kinetics during incubation at 30-50°C. The rate of decrease in the water holding capacity of the myofibrils was about half of that of denaturation of the myofibrillar EDTA-ATPase.