Alanopine dehydrogenase (ADH) and both ADH and strombine dehydrogenase (SDH) are respectively the major opine dehydrogenases in the gills and mantle of hard clam under normoxia. However, ADH, octopine dehydrogenase (ODH), and SDH are the predominant opine dehydrogenases in the foot and adductor of the hard clam under normoxia. After anoxic exposure, significant increases in the activities of opine dehydrogenases in the gills were observed for ADH as well as SDH and lactate dehydrogenase (LDH). However, the activities of ADH and SDH in the mantle were not responsive to anoxic exposure. Activities of ADH, ODH, SDH, and LDH in the foot were not affected by 3 h of anoxic exposure, but were significantly increased after 6 h of anoxic exposure. The major species of opine dehydrogenases in the adductor were the same as those in the foot. The activities of LDH and all opine dehydrogenases except taurine dehydrogenase (TDH) in the adductor were significantly stimulated by anoxic exposure, and their maximum activities were found by 3 h of anoxic exposure. After anoxic exposure, the rates of increases in the activities of ADH, ODH, and SDH in the adductor ranged from 150 to 230 mU/mg/h were much higher than those in the gills, mantle, and foot. Therefore, these opine dehydrogenases play an important role in the anaerobic metabolism of the adductor in the hard clam.

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