Kinetic characterization of the gill (Na+, K+)-ATPase in a hololimnetic population of the diadromous Amazon River shrimp Macrobrachium amazonicum (Decapoda, Palaemonidae)

We provide a kinetic characterization of (Na+, K+)-ATPase activity in a posterior gill microsomal fraction from a hololimnetic population of the diadromous Amazon River shrimp Macrobrachium amazonicum. Sucrose density gradient centrifugation reveals two distinct membrane fractions showing considerable (Na+, K+)ATP-ase activity, but also containing other microsomal ATPases. Only a single immune-reactive (Na+, K+)-ATPase with M-r of approximate to 110 kDa is present that hydrolyzes ATP with V-M = 130.3 +/- 4.8 nmol Pi min(-1) mg protein(-1) and K-0.5 = 0.065 +/- 0.00162 mmol L-1, exhibiting site-site interactions. Stimulation by Na+ (V-M = 127.5 +/- 5.3 nmol Pi min(-1) mg protein(-1), K-0.5 = 5.3 +/- 0.42 mmol L-1), Mg2+ (V-M = 130.6 +/- 6.8 nmol Pi min(-1) mg protein(-1), K-0.5 = 0.33 +/- 0.042 mmol L-1), K+ (V-M = 126.7 +/- 7.7 nmol Pi min(-1) mg protein(-1), K-0.5 = 0.65 +/- 0.0079 mmol L-1) and NH4+ (V-M = 134.5 +/- 8.6 nmol Pi min(-1) mg protein(-1), K-0.5 = 1.28 +/- 0.44 mmol L-1) also obeys cooperative kinetics. Ouabain (K-1 = 0.18 +/- 0.058 mmol L-1) inhibits total ATPase activity by approximate to 70%. This study reveals considerable differences in the kinetic characteristics of the gill (Na+, K+)-ATPase in a hololimnetic population that appear to result from the adaptation of diadromous Macrobrachium amazonicum populations to different limnic habitats.