AJP - Regulatory, Integrative and Comparative Physiology, Vol 246, Issue 4 487-R494, Copyright © 1984 by American Physiological Society
Why bluefin tuna have warm tummies: temperature effect on trypsin and chymotrypsin
E. D. Stevens and J. M. McLeese
Giant bluefin tuna warm their viscera during and after a meal. The cecum of
a 500-kg bluefin weighs about 9 kg and contains about 20,000 pyloric ceca,
each about 10 cm long and 1.5 mm diam. Trypsin was assayed with
alpha-benzoyl-DL-arginine-p-nitroanilide HCl and chymotrypsin with
glutaryl-L-phenylalanine-p-nitroaniline. The effects of pH on specific
activity over the range 7.5-9.5 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 (Q10 ca. 2 over temperature range of physiological
significance), whereas Km was constant over the same temperature range. The
advantage of the warm cecum 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.
