Differences in tissue-specific control of phosphofructokinase and pyruvate kinase activity in the cockle, Cardium tuberculatum during exercise and anoxia

Abstract

1. 1. Kinetic properties of phosphofructokinase (PFK) and pyruvate kinase (PK) were used for identification of tissue-specific isoenzymes and their anaerobic modifications in the jumping cockle ( Cardium tuberculatum). 2. 2. PFK in foot muscle and gills of normoxic animals has nearly identical kinetic properties ( S 0.5(F6P) = 1.1 mM, N H = 2.2; K A(AMP) = 0.2 mM and K A(F-2,6-P 2) = 4.6 μM). 3. 3. After anoxia the PFK in gills exhibited a reduced substrate affinity for F6P, and for the enzyme of both tissues the activating effect of AMP was diminished. 4. 4. PK from foot muscle and gills differed in the affinity for the substrate phosphoenolpyruvate ( S 0.5 = 0.13 vs 0.25 mM PEP, respectively), in the effect of l-alanine on the PEP affinity ( S 0.5 = 0.25 vs 1.1 mM PEP at 1 mM alanine), and the affinity for the activator FBP ( K A = 0.64 vs 10.9 μM FBP). 5. 5. After anoxia, the PEP affinity of the PK in gills was lowered and the inhibitory influence of alanine was increased, while anoxic modification of PK properties in muscle tissue was indicated by the reduced effectiveness of FBP in reversing alanine inhibition. 6. 6. The anoxic modification of modulator affinities of the enzymes in muscle tissue preserves the opportunity of high glycolytic flux during exercise, while the direct alteration of substrate affinities causes tight regulation.