Properties of enzymes from mammalian hibernators: Structure function relationships
The examination of four enzymes, glutathione S-transferase (GST), glutathione reductase (GR), aspartate aminotransferase (AspAT), and glutamate dehydrogenase (GDH), from two hibernators Cynomys leucurus andSpermophilus richardsonii were used to show three different responses to a hibernating life style. The production of a new (isozyme) of GST, alpha-class, in the liver and muscle tissues of Cynomys leucurus. N-terminal and amino acid compositions show strong homology alpha-class GSTs from a variety of species. The kinetic profile and structural studies suggest that this isozyme is similar to other alpha-class GSTs. PDM 18 showed a broader temperature optima and lower thermal stability compared to a comparable rabbit enzyme. A different form of GDH was found in the liver tissue of Spermophilus richardsonii in the hibernating animal. This new isozyme of GDH differed from the nonhibernating and bovine enzyme in both physical and kinetic parameters. There is a shift in the directional preference between the two ground squirrel forms of the enzyme in the presence of GTP, ATP, AMP. Further kinetic differences are also reflected in I50, Km, and Ka values between the two ground squirrel isozymes. The N-terminal sequence of the two isozymes is identical over the first 12 residues; there are differences in the molecular weight by size exclusion chromatography, and retention time on reverse phase HPLC suggesting small differences in the polypeptide chain. The final observed case was that there were no substantial kinetic and minor structural changes between the enzyme from the hibernator and from a nonhibernator. This was seen with two enzymes from the study GR (from prairie dog) and AspAT (from ground squirrel).