Occurrence of alanine racemase in crustaceans and the changes of the properties during seawater acclimation of crayfish

Alanine racemase activity was detected in the muscle and hepatopancreas of six macruran species. Optimal pH was around 8.5 irrespective of species and tissues. Apparent Michaelis constants ranged from 48 to 157 mM for muscle enzyme and 35 to 239 mM for hepatopancreas enzyme. The enzyme specifically catalyzed the racemization of D- and L-alanine. The enzyme did not require pyridoxal 5'-phosphate as well as FAD as a cofactor. Pyruvate and L-alanine showed strong inhibition in the direction of D to L. During seawater acclimation of crayfish Procambarus clarkii; alanine racemase activity increased about twice in muscle and 1.5 rimes in hepatopancreas. Michaelis constant, on the other hand, decreased 33% for muscle enzyme and 65% for hepatopancreas enzyme, suggesting the increase of substrate affinity during seawater acclimation The activity in the physiological pH range (6.5-7.5) also increased with increasing salinity. Copyright (C) 1996 Elsevier Science Inc.