Why bluefin tuna have warm tummies: temperature effect on trypsin and chymotrypsin

Giant bluefin tuna (Thunnus thynnus) warm their viscera during and after a meal. The caecum of a 500-kg bluefin weighs about 9 kg and contains about 20 000 pyloric caeca, each about 10 cm long and 1.5 mm diameter. Trypsin was assayed with α-benzoyl-DL-arginine-p-nitroanilide HCl and chymotrypsin with glutaryl-L-phenylalanine-p-nitroaniline. The effects of pH on specific activity over the range 7.5 to 9.5 were negligible relative to temperature effects. Specific activity and maximal reaction velocity extrapolated from a Lineweaver-Burke plot (Vmax) increased with an increase in temperature in a similar fashion, whereas Km was constant over the same temperature range. The advantage of the warm caecum is that protein is digested in about one-third the time, so that these tuna can process about three times as much food per day.