The thermal inactivation of the hepatic cytosolic Ah receptor was studied in vitro for several immature male rodents. The activation energies for receptor inactivation in C57BL/6 mice, Mongolian gerbils, golden Syrian hamsters, Hartley guinea-pigs, Sprague-Dawley rats and Wistar rats were 170, 142, 112, 131, 120 and 112 kJ/mol, respectively. The magnitude of the activation parameters pointed to a substantial change on inactivation, but not to complete unfolding of the protein. Statistical analysis indicated that attempts to interpret these results in terms of receptor heterology should be treated with caution. Among the species studied, the Ah receptor from the mouse offered the best possibility for in vitro studies at low temperature, free from the problem of thermal inactivation.
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