title: Synergistic stimulation by potassium and ammonium of K(+)-phosphatase activity in gill microsomes from the crab Callinectes ornatus acclimated to low salinity: novel property of a primordial pump.
abstract: We provide an extensive characterization of the modulation by p-nitrophenylphosphate, Mg²⁺, Na⁺, K(+), Rb⁺, NH(4)(+) and pH of gill microsomal K⁺-phosphatase activity in the posterior gills of Callinectes ornatus acclimated to low salinity (21‰). The synergistic stimulation by K⁺ and NH(4)(+) of the K⁺-phosphatase activity is a novel finding, and may constitute a species-specific feature of K(+)/NH(4)(+) interplay that regulates crustacean gill (Na⁺, K⁺)-ATPase activity. p-Nitrophenylphosphate was hydrolyzed at a maximum rate (V) of 69.2 ± 2.8nmolPimin⁻¹mg⁻¹ with K(0.5)=2.3 ± 0.1mmolL(-1), obeying cooperative kinetics (n(H)=1.7). Stimulation by Mg²⁺ (V=70.1 ± 3.0nmolPimin⁻¹mg⁻¹, K(0.5)=0.88 ± 0.04mmolL⁻¹), K⁺ (V=69.6 ± 2.7nmolPimin⁻¹mg⁻¹, K(0.5)=1.60 ± 0.07mmolL⁻¹) and NH(4)(+) (V=90.8 ± 4.0nmolPimin⁻¹mg⁻¹, K(0.5)=9.2 ± 0.3mmol L⁻¹) all displayed site-site interaction kinetics. In the presence of NH(4)(+), enzyme affinity for K⁺ unexpectedly increased by 7-fold, while affinity for NH(4)(+) was 28-fold greater in the presence than absence of K⁺. Ouabain partially inhibited K⁺-phosphatase activity (K(I)=320 ± 14.0μmolL⁻¹), more effectively when NH(4)(+) was present (K(I)=240 ± 12.0μmolL⁻¹). We propose a model for the synergistic stimulation by K⁺ and NH(4)(+) of the K⁺-phosphatase activity of the (Na⁺, K⁺)-ATPase from C. ornatus posterior gill tissue.
authors.affiliation: Departamento de Biologia Molecular, Centro de Ciências Exatas e da Natureza, Universidade Federal da Paraíba, Brazil.
authors.forename: Daniela P
authors.initials: DP
authors.lastname: Garçon
authors.forename: Malson N
authors.initials: MN
authors.lastname: Lucena
authors.forename: Marcelo R
authors.initials: MR
authors.lastname: Pinto
authors.forename: Carlos F L
authors.initials: CF
authors.lastname: Fontes
authors.forename: John C
authors.initials: JC
authors.lastname: McNamara
authors.forename: Francisco A
authors.initials: FA
authors.lastname: Leone
mesh_terms: D000641:Ammonia / Q000819:agonists / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D060829:Arthropod Proteins / Q000737:chemistry* / Q000378:metabolism; D003386:Brachyura / Q000201:enzymology*; D005880:Gills / Q000201:enzymology*; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology*; D009596:Nitrophenols / Q000737:chemistry; D009943:Organophosphorus Compounds / Q000737:chemistry; D011188:Potassium / Q000819:agonists / Q000737:chemistry* / Q000378:metabolism; D054712:Salinity; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry* / Q000378:metabolism
chemical_list: D060829:Arthropod Proteins; D009596:Nitrophenols; D009943:Organophosphorus Compounds; C008644:nitrophenylphosphate; D000641:Ammonia; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium