The effects of aestivation on the catalytic and regulatory properties of pyruvate kinase from Helix aspersa

Abstract

1. 1. Pyruvate kinase was partially purified from the foot, mantle, and digestive gland of active and aestivating snails. 2. 2. At pH 7.0 the apparent K m values for phosphoenolpyruvate (PEP) were 0.064 mmol/l for the enzyme from foot and 0.071 mmol/l for the enzyme from mantle; those for ADP were 0.35 mmol/l for the foot enzyme and 0.33 mmol/l for the mantle enzyme. 3. 3. Both enzymes were inhibited by alanine, and this could be reversed by fructose 1,6-bisphosphate (FBP), although FBP alone was a weak activator. 4. 4. Decreasing the pH to 6.5 markedly increased the inhibition by alanine and reduced the response to FBP. 5. 5. The enzymes from these tissues of aestivating snails showed a small decrease in their affinity for PEP and a small increase in the effectiveness of alanine as an inhibitor. 6. 6. These changes are indicative of a down-regulation of this enzyme which is consistent with the observations in other species during metabolic depression. 7. 7. In contrast the enzyme from the digestive gland of active animals showed sigmoidal saturation kinetics for PEP with a S 0.5 of 1.2 mmol/l, but had a markedly higher affinity for PEP, S 0.5 = 0.20 mmol/l during aestivation. This may be indicative of other metabolic changes occurring in the digestive gland.