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

Kinetic Analysis of Gill (Na+,K+)-ATPase Activity in Selected Ontogenetic Stages of the Amazon... 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+ (K 0.5 = 0.91 ± 0.04 mmol L−1) in decapodid III than in other stages; NH4 + had no modulatory effect. The affinity for Na+ (K 0.5 = 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. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Membrane Biology Springer Journals

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

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Publisher
Springer-Verlag
Copyright
Copyright © 2012 by Springer Science+Business Media, LLC
Subject
Life Sciences; Biochemistry, general; Human Physiology
ISSN
0022-2631
eISSN
1432-1424
D.O.I.
10.1007/s00232-012-9431-9
Publisher site
See Article on Publisher Site

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+ (K 0.5 = 0.91 ± 0.04 mmol L−1) in decapodid III than in other stages; NH4 + had no modulatory effect. The affinity for Na+ (K 0.5 = 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.

Journal

The Journal of Membrane BiologySpringer Journals

Published: Apr 28, 2012

References

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