Differences in conformation stability of lactate dehydrogenase from skeletal muscles of fishes adapted to different temperatures

The effect of temperature on the secondary structure of lactate dehydrogena se from skeletal muscles of leaches adapted for 25 days at 5 degrees C (col d enzyme) and 18 degrees C (warm enzyme) was studied. The two forms of lact ate dehydrogenase have a different course of thermal denaturation, and thes e differences are determined by the melting of alpha-helical structures. Th e melting of alpha-helices of the cold enzyme exhibits a high cooperativity and occurs in a temperature range 70-85 degrees C. The melting of warm lac tate dehydrogenase is observed in a broader temperature (40-85 degrees C) a nd consists of two phases: predenaturation in the range from 40 to 75 degre es C and cooperative melting in the range from 75 to 85 degrees C.