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

Leonardo M. Fabri,M. N. Lucena,D. P. Garçon,Cintya M. Moraes,J. McNamara,F. A. Leone

Published 2019 in Comparative Biochemistry and Physiology Part B Comparative Biochemistry

ABSTRACT

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 Mr of ≈110 kDa is present that hydrolyzes ATP with VM = 130.3 ± 4.8 nmol Pi min-1 mg protein-1 and K0.5 = 0.065 ± 0.00162 mmol L-1, exhibiting site-site interactions. Stimulation by Na+ (VM = 127.5 ± 5.3 nmol Pi min-1 mg protein-1, K0.5 = 5.3 ± 0.42 mmol L-1), Mg2+ (VM = 130.6 ± 6.8 nmol Pi min-1 mg protein-1, K0.5 = 0.33 ± 0.042 mmol L-1), K+ (VM = 126.7 ± 7.7 nmol Pi min-1 mg protein-1, K0.5 = 0.65 ± 0.0079 mmol L-1) and NH4+ (VM = 134.5 ± 8.6 nmol Pi min-1 mg protein-1, K0.5 = 1.28 ± 0.44 mmol L-1) also obeys cooperative kinetics. Ouabain (KI = 0.18 ± 0.058 mmol L-1) 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.

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