Affordable Access

K+and NH4+modulate gill (Na+, K+)-ATPase activity in the blue crab,Callinectes ornatus: Fine tuning of ammonia excretion

Authors
Journal
Comparative Biochemistry and Physiology Part A Molecular & Integrative Physiology
1095-6433
Publisher
Elsevier
Publication Date
Volume
147
Issue
1
Identifiers
DOI: 10.1016/j.cbpa.2006.12.020
Keywords
  • Ammonium Ion
  • Atp
  • Crustacean Gill
  • Microsomal Fraction
  • (Na+
  • K+)-Atpase
  • Ouabain
  • Brachyuran Crab
  • Callinectes Ornatus
Disciplines
  • Biology

Abstract

Abstract To better comprehend the mechanisms of ionic regulation, we investigate the modulation by Na +, K +, NH 4 + and ATP of the (Na +, K +)-ATPase in a microsomal fraction from Callinectes ornatus gills. ATP hydrolysis obeyed Michaelis–Menten kinetics with K M = 0.61 ± 0.03 mmol L − 1 and maximal rate of V = 116.3 ± 5.4 U mg − 1. Stimulation by Na + ( V = 110.6 ± 6.1 U mg − 1; K 0.5 = 6.3 ± 0.2 mmol L − 1), Mg 2+ ( V = 111.0 ± 4.7 U mg − 1; K 0.5 = 0.53 ± 0.03 mmol L − 1), NH 4 + ( V = 173.3 ± 6.9 U mg − 1; K 0.5 = 5.4 ± 0.2 mmol L − 1) and K + ( V = 116.0 ± 4.9 U mg − 1; K 0.5 = 1.5 ± 0.1 mmol L − 1) followed a single saturation curve, although revealing site–site interactions. In the absence of NH 4 +, ouabain ( K I = 74.5 ± 1.2 μmol L − 1) and orthovanadate inhibited ATPase activity by up to 87%; the inhibition patterns suggest the presence of F 0F 1 and K +-ATPases but not Na +-, V- or Ca 2+-ATPase as contaminants. (Na +, K +)-ATPase activity was synergistically modulated by K + and NH 4 +. At 10 mmol L − 1 K +, increasing NH 4 + concentrations stimulated maximum activity to V = 185.9 ± 7.4 U mg − 1. However, at saturating NH 4 + (50 mmol L − 1), increasing K + concentrations did not stimulate activity further. Our findings provide evidence that the C. ornatus gill (Na +, K +)-ATPase may be particularly well suited for extremely efficient active NH 4 + excretion. At elevated NH 4 + concentrations, the enzyme is fully active, regardless of hemolymph K + concentration, and K + cannot displace NH 4 + from its exclusive binding sites. Further, the binding of NH 4 + to its specific sites induces an increase in enzyme apparent affinity for K +, which may contribute to maintaining K + transport, assuring that exposure to elevated ammonia concentrations does not lead to a decrease in intracellular potassium levels. This is the first report of modulation by ammonium ions of C. ornatus gill (Na +, K +)-ATPase, and should further our understanding of NH 4 + excretion in benthic crabs.

There are no comments yet on this publication. Be the first to share your thoughts.

Statistics

Seen <100 times
0 Comments

More articles like this

K+ and NH4(+) modulate gill (Na+, K+)-ATPase activ...

on Comparative Biochemistry and P... May 2007

Na+, K+-ATPase activity in gill microsomes from th...

on Comparative Biochemistry and P... Jan 01, 2009

Na(+), K(+)-ATPase activity in gill microsomes fro...

on Comparative Biochemistry and P... Jan 01, 2009

Na⁺,K⁺-ATPase activity in the posterior gills of t...

on The Journal of Membrane Biolog... November 2011
More articles like this..