Intracellular Buffering by Dipeptides at High and Low Temperature in the Blue Crab Callinectes Sapidus

Intracellular buffering is provided mainly by bicarbonate, phosphates and proteins (see Burton, 1978). A part may also be played by free histidine and small peptides containing histidine. Although the free histidine content of most animal tissues is low, a variety have been found to possess substantial amounts of histidine-containing dipeptides, most commonly N-β-alanyl-L-histidine, either without substitutions (carnosine) or methylated at the 1-position (anserine) or at the 3-position (ophidine or balenine). At 25°C the pK of carnosine is 6·83 whereas that of anserine is 7·04, so the combination of appropriate pK and high concentration leads to significant intracellular buffer action.