THE THERMOSTABILITY OF HEMOGLOBINS FROM THE HOT-SPRING FISH, OREOCHROMIS-ALCALICUS GRAHAMI - COMPARISONS WITH ANTARCTIC AND TEMPERATE SPECIES

1. The thermostability of haemoglobin was measured in three species of fish living at different environmental temperatures (ET). 2. The time (min) for 50% denaturation (T(1/2)d) of the haemoglobin at 2 mg ml(-1 ) in 50 mM phosphate buffer, pH 7.3 was 46.4 +/- 1.7 for Oreochromis a lcalicus grahami (ET, 35 to 42 degrees C), 43.1 +/- 1.9 for Oreochromi s ni[oticus (ET, 18 to 26 degrees C) and 19.2 +/- 0.3 for the Antarcti c teleost, Notothenia coriiceps (ET, -1.5 to 1 degrees C) (Mean +/- SE M, N = 5-7 preparations). In contrast, T(1/2)d for haemoglobin from bi rds and mammals is usually in excess of 500 min. 3. These results sugg est that the]ower thermostability of haemoglobins in fish relative to birds and mammals is not solely a function of differences in body temp erature.