Protein phosphatase responses during freezing and thawing in wood frogs: Control of liver cryoprotectant metabolism

Freezing at -2.5 degrees C induced a 50 % increase in total protein phospha tase type 1 (PP-1) activity in Rana sylvatica liver within 20 min and a 130 % increase in active enzyme. Activity remained high over a 12 h freeze but began to fall again after 4 h thawing. PP-1 responded similarly to dehydra tion stress but did not change under anoxia stress. Freezing also caused a translocation of PP-1; alpha and delta isoforms were found with glycogen pa rticles in control liver but were free in the cytoplasm in frozen frogs. Th is could prevent PP-1 from inhibiting glycogenolysis during the freeze-indu ced synthesis of glucose as a cryoprotectant. Protein phosphatase types 2A and 2C in liver responded differently. PP-2C rose by 37 % after 1 h freezin g but PP-2A rose by 64% only after 12 h. The pattern of PP-2A and 2C respon ses was different in muscle, activities rising within 5 min post-nucleation .