The effect of cations on the specific activities of pyruvate kinase and glucose-6-phosphate dehydrogenase of Luidia clathrata (say) (Echinodermata: Asteroidea)

Abstract

1. 1. The combined effect of cations (Na +, K +, Ca 2+ and Mg 2+) on the specific activities of pyruvate kinase (PK) and glucose-6-phosphate dehydrogenase (G-6-PDH) were examined in the pyloric caeca, gonads and tube feet of adult Luidia clathrata. 2. 2. Cation concentrations were based on previously determined intracellular values from individuals that had been exposed to 15, 25 and 35% salinity for 1 week. 3. 3. Increases in cationic strength resulted in decreases in specific activity for both enzymes in all tissues. As cationic strength increased, decreases in specific activity were greater for G-6-PDH than PK under similar assay conditions. 4. 4. The relative sensitivity of PK to changes in cation concentration may ensure the stability of the enzyme's catalytic and regulatory functions, while the greater relative sensitivity of G-6-PDH to cations could alter the organism's anabolic capacity.