The thermostability of haemoglobins from the hot-spring fish, Oreochromis alcalicus grahami: comparisons with Antarctic and temperate species

The thermostability of haemoglobin was measured in three species of fish living at different environmental temperatures (ET). The time (min) for 50% denaturation (T sub(1/2)d) of the haemoglobin at 2 mg ml super(-1) in 50 mM phosphate buffer, pH 7.3 was 46.4 plus or minus 1.7 for Oreochromis alcalicus grahami (ET, 35 to 42 degree C), 43.1 plus or minus 1.9 for Oreochromis niloticus (ET, 18 to 26 degree C) and 19.2 plus or minus 0.3 for the Antarctic teleost, Notothenia coriiceps (ET, -1.5 to 1 degree C) (Mean plus or minus SEM, N = 5-7 preparations). In contrast, T sub(1/2)d for haemoglobin from birds and mammals is usually in excess of 500 min. These results suggest that the lower thermostability of haemoglobins in fish relative to birds and mammals is not solely a function of differences in body temperature.