Abstract
The effects of anoxia on pyruvate kinases (PK) from the heart and foot muscle of Concholepas concholepas, as well as the presence and levels of phosphoenolpyruvate carboxykinase (PEPCK) in the aerobic and anoxic tissues, were examined. In response to anoxia, the maximal activity of pyruvate kinase decreased in the heart but was not altered in the foot muscle. Phosphoenolpyruvate carboxykinase was not detected in the foot muscle and anoxic stress had no effect on the activity of this enzyme in the heart tissue. Anoxic stress altered the kinetic and regulatory properties of heart PK without any change in the foot muscle enzyme. Anoxic heart PK was much more dependent of fructose 1,6‐diphosphate for significant activity at low concentrations of phos‐phoenolpyruvate and had a higher sensitivity to inhibition by alanine and ATP than the aerobic enzyme from. All changes were reversed when the animals were transferred to well‐aerated seawater. The results are compatible with the operation of a succinate pathway of glycogen degradation during prolonged environmental anoxia in the heart, but not in the foot muscle tissue of C. concholepas.