title: Kinetic analysis of gill (Na⁺,K⁺)-ATPase activity in selected ontogenetic stages of the Amazon River shrimp, Macrobrachium amazonicum (Decapoda, Palaemonidae): interactions at ATP- and cation-binding sites.
abstract: We investigated modulation by ATP, Mg²⁺, Na⁺, K⁺ and NH₄⁺ and inhibition by ouabain of (Na⁺,K⁺)-ATPase activity in microsomal homogenates of whole zoeae I and decapodid III (formerly zoea IX) and whole-body and gill homogenates of juvenile and adult Amazon River shrimps, Macrobrachium amazonicum. (Na⁺,K⁺)-ATPase-specific activity was increased twofold in decapodid III compared to zoea I, juveniles and adults, suggesting an important role in this ontogenetic stage. The apparent affinity for ATP (K(M) = 0.09 ± 0.01 mmol L⁻¹) of the decapodid III (Na⁺,K⁺)-ATPase, about twofold greater than the other stages, further highlights this relevance. Modulation of (Na⁺,K⁺-ATPase activity by K⁺ also revealed a threefold greater affinity for K⁺ (K₀.₅ = 0.91 ± 0.04 mmol L⁻¹) in decapodid III than in other stages; NH₄⁺ had no modulatory effect. The affinity for Na⁺ (K₀.₅ = 13.2 ± 0.6 mmol L⁻¹) of zoea I (Na⁺,K⁺)-ATPase was fourfold less than other stages. Modulation by Na⁺, Mg²⁺ and NH₄⁺ obeyed cooperative kinetics, while K⁺ modulation exhibited Michaelis-Menten behavior. Rates of maximal Mg²⁺ stimulation of ouabain-insensitive ATPase activity differed in each ontogenetic stage, suggesting that Mg²⁺-stimulated ATPases other than (Na⁺,K⁺)-ATPase are present. Ouabain inhibition suggests that, among the various ATPase activities present in the different stages, Na⁺-ATPase may be involved in the ontogeny of osmoregulation in larval M. amazonicum. The NH₄⁺-stimulated, ouabain-insensitive ATPase activity seen in zoea I and decapodid III may reflect a stage-specific means of ammonia excretion since functional gills are absent in the early larval stages.
authors.affiliation: Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Avenida Bandeirantes, 3900 Ribeirão Prêto, SP 14040-901, Brazil. fdaleone@ffclrp.usp.br
authors.forename: Francisco Assis
authors.initials: FA
authors.lastname: Leone
authors.forename: Douglas Chodi
authors.initials: DC
authors.lastname: Masui
authors.forename: Thais Milena
authors.initials: TM
authors.lastname: de Souza Bezerra
authors.forename: Daniela Pereira
authors.initials: DP
authors.lastname: Garçon
authors.forename: Wagner Cotroni
authors.initials: WC
authors.lastname: Valenti
authors.forename: Alessandra Silva
authors.initials: AS
authors.lastname: Augusto
authors.forename: John Campbell
authors.initials: JC
authors.lastname: McNamara
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002412:Cations; D033364:Decapoda / Q000254:growth & development* / Q000378:metabolism*; D005880:Gills / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D011485:Protein Binding; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D002412:Cations; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase