GLUCOSE-6-PHOSPHATE-DEHYDROGENASE FROM THE BLOOD-CELLS OF 2 ANTARCTICTELEOSTS - CORRELATION WITH COLD ADAPTATION

Glucose-6-phosphate dehydrogenase (G6PD) has been purified from the bl ood of two Antarctic teleost species, i.e., from the erythrocytes of D issostichus mawsoni (family Nototheniidae), and from the plasma and ce lls of haemoglobinless Chionodraco hamatus (family Channichthyidae). T he specific activities in haemolysates of Antarctic blood cells appear higher than that of a lysate of human erythrocytes. The two Antarctic enzymes have an apparent subunit molecular mass slightly higher than that of human G6PD; the electrophoretic behaviour on cellulose acetate is similar. Both Antarctic enzymes are irreversibly heat inactivated through a biphasic process. K-m for glucosed-phosphate (G6P) does not vary significantly with temperature, whereas K-m for NADP increases at increasing temperature. k(cat) increases with temperature, with a bre ak point at 35 degrees C (in human G6PD, the break point is at 15 degr ees C). Thermodynamic and kinetic characterisation indicate that the c atalytic performance of the enzyme of cold-adapted fish, at temperatur es typical of their habitat, is more efficient than that displayed by G6PD from a temperate organism.