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 of ≈110 kDa is present that hydrolyzes ATP with V = 130.3 ± 4.8 nmol Pi min mg protein and K = 0.065 ± 0.00162 mmol L, exhibiting site-site interactions. Stimulation by Na (V = 127.5 ± 5.3 nmol Pi min mg protein, K = 5.3 ± 0.42 mmol L), Mg (V = 130.6 ± 6.8 nmol Pi min mg protein, K = 0.33 ± 0.042 mmol L), K (V = 126.7 ± 7.7 nmol Pi min mg protein, K = 0.65 ± 0.0079 mmol L) and NH (V = 134.5 ± 8.6 nmol Pi min mg protein, K = 1.28 ± 0.44 mmol L) also obeys cooperative kinetics. Ouabain (K = 0.18 ± 0.058 mmol L) inhibits total ATPase activity by ≈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.