A carrier enzyme basis for ammonium excretion in teleost gill. NH+4-stimulated Na-dependent ATPase activity in Opsanus beta.
1. Branchial Na+K+-ATPase specific activity is some 20% greater in hyposaline adapted Opsanus beta than in SW specimens. 2. Ouabain insensitive ATPase (Mg2+-ATPase) specific activities were similar, while whole body activity differences in low salinity and SW adapted fish could be accounted for by the 30% difference in extractable gill protein. 3. NH+4 ion was 15% more effective at dephosphorylation of the microsomal Na-dependent phosphoenzyme than either Rb+ or K+, and revealed a maximal ATPase affinity (Km = 0.2 mM) within the physiological range of blood [K+]. 4. Similar properties as pH optima, ATP and Mg2+ Km's, ouabain sensitivity, percent recoveries and subcell distribution indicated that the NH+4-stimulation acts through the Na+ K+-ATPase carrier enzyme and may be responsible for the Na+/NH+4 exchange in Opsanus beta.
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase; D005399:Fishes / Q000378:metabolism*; D005880:Gills / Q000201:enzymology*; D010766:Phosphorylation; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013347:Subcellular Fractions / Q000201:enzymology
D000644:Quaternary Ammonium Compounds; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D000254:Sodium-Potassium-Exchanging ATPase