| k+ and nh4(+) modulate gill (na+, k+)-atpase activity in the blue crab, callinectes ornatus: fine tuning of ammonia excretion. | to better comprehend the mechanisms of ionic regulation, we investigate the modulation by na+, k+, nh4(+) and atp of the (na+, k+)-atpase in a microsomal fraction from callinectes ornatus gills. atp hydrolysis obeyed michaelis-menten kinetics with km=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); k0.5=6.3+/-0.2 mmol l(-1)), mg2+ (v=111.0+/-4.7 u mg(-1); k0.5=0.53+/-0.03 mmol l(-1)), nh4(+) (v=173.3+/-6.9 u mg(-1); k0.5=5.4+/-0.2 mmo ... | 2007 | 17276114 |
| hemolymph ionic regulation and adjustments in gill (na+, k+)-atpase activity during salinity acclimation in the swimming crab callinectes ornatus (decapoda, brachyura). | we evaluate hemolymph osmotic and ionic regulatory abilities and characterize a posterior gill microsomal (na+, k+)-atpase from the marine swimming crab, callinectes ornatus, acclimated to 21 per thousand or 33 per thousand salinity. c. ornatus is isosmotic after acclimation to 21 per thousand but is hyposmotic at 33 per thousand salinity; hemolymph ions do not recover initial levels on acclimation to 21 per thousand salinity but are anisoionic compared to ambient concentrations, revealing modes ... | 2009 | 19422928 |
| Na?,K?-ATPase activity in the posterior gills of the blue crab, Callinectes ornatus (Decapoda, Brachyura): modulation of ATP hydrolysis by the biogenic amines spermidine and spermine. | 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 concentratio ... | 2011 | 21972069 |