We investigated the effect of the exogenous polyamines spermine, spermidine and putrescine on modulation by ATP, K+, Na+, NH4 + and Mg2+ and on inhibition by ouabain of posterior gill microsomal Na+,K+-ATPase activity in the blue crab, Callinectes ornatus, acclimated to a dilute medium (21‰ salinity). This is the first kinetic demonstration of competition between spermine and spermidine for the cation sites of a crustacean Na+,K+-ATPase. Polyamine inhibition is enhanced at low cation concentrations: spermidine almost completely inhibited total ATPase activity, while spermine inhibition attained 58%; putrescine had a negligible effect on Na+,K+-ATPase activity. Spermine and spermidine affected both V and K for ATP hydrolysis but did not affect ouabain-insensitive ATPase activity. ATP hydrolysis in the absence of spermine and spermidine obeyed Michaelis–Menten behavior, in contrast to the cooperative kinetics seen for both polyamines. Modulation of V and K by K+, Na+, NH4 + and Mg2+ varied considerably in the presence of spermine and spermidine. These findings suggest that polyamine inhibition of Na+,K+-ATPase activity may be of physiological relevance to crustaceans that occupy habitats of variable salinity.
The Journal of Membrane Biology – Springer Journals
Published: Oct 5, 2011
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