Pyruvate kinase in muscle extracts of the sea mussel Mytilus edulis L

Abstract

1. 1. Pyruvate kinase activity in fresh extracts from the posterior adductor muscle of the sea mussel, Mytilus edulis, shows allosteric properties in contrast to skeletal pyruvate kinases of mammals.

2. 2. The Hill plot at [PEP]* = ∞ shows positive co-operativity (nH = 1·3) with respect to PEP.

3. 3. The sigmoidicity of the substrate concentration-velocity curve is strongly increased in the presence of alanine (inhibition). The Hill coefficient increases from 1·3 to 1·8 whereas the Km app. for PEP changes from 0·65 to 1·58 mM.

4. 4. Pyruvate kinase activity is also strongly inhibited by ATP.

5. 5. Inhibition of pyruvate kinase activity by alanine and ATP is counteracted by FDP.

6. 6. The properties of pyruvate kinase might explain why a part of PEP is available for succinate production during anaerobic glycolysis.