[Lipoamide dehydrogenase, citrate synthase and beta-hydroxyacyl-CoA-dehydrogenase in skeletal muscle. IX. The influence of the rate of thawing on activity and subcellular distribution in fast and slow frozen bovine muscle].

Samples of bovine muscle (post rigor) were frozen at -30 degrees C at two different rates (1.27 min/degrees C and 13.10 min/degrees C) and thawed at different rates between 1.6 (22 degrees C) and 430 min/degrees C (0 degrees C). The activities of the mitochondrial enzymes lipoamide dehydrogenase, citrate synthase, and beta-hydroxyacyl-CoA-dehydrogenase were determined in the supernatant of the tissue homogenate in phosphate buffer (total activity) and in the press juice of the intact tissue (activity in the sarcoplasma). The rate of thawing did not show a significant influence on total enzyme activities. In most cases, however, slow thawing caused a greater release of the enzymes from the mitochondria into the sarcoplasmic fluid than fast thawing, this effect being apparently independent of the rate of freezing. The greater damage to mitochondrial membranes upon slow thawing cannot be due to a longer exposure of the muscle cell to increased ionic strength in the non-freezable part of the cell water at the "critical" temperature around -3 degrees C because freezing of muscle samples at -3 degrees C and incubating them at -3 degrees C for five days resulted neither in changes of the total enzyme activities nor in a release of the three mitochondrial enzymes. From these results it is concluded that the influence of thawing rate on the damage to muscle mitochondria is probably not due to ionic effects or to recrystallization phenomena in the ice phase.