Inhibition of Na+,K+-ATPase in Penaeus indicus postlarvae by lead

The plasma membrane/mitochondrial fractions of Penaeus indicus postlarvae c ontain Mg2+-dependent ATPase, Na+,K+-stimulated ATPase, Na+-stimulated ATPa se and K+-stimulated ATPase. The Na+,K+-activated, Mg2+-dependent ATPase wa s investigated further in relation to different pH and temperature conditio ns, and at various concentrations of protein, ouabain, ATP and ions in the incubation medium. In vitro and in vivo effects of lead were studied on the enzyme activity. In vitro lead inhibited the enzyme activity in a concentr ation-dependent manner with an IC50 value of 204.4 muM. In correlation with in vitro studies, in vivo investigations (both concentration and time depe ndent) of lead also indicated a gradual inhibition in enzyme activity. A ma ximum decrease of 85.3% was observed at LC50 (7.2 ppm) of lead for concentr ation-dependent experiments. In time-dependent studies, the decrease was ma ximal (81.7%) at 30 days of sublethal exposure (1.44 ppm). In addition, the substrate- and ion-dependent kinetics of Na+,K+-ATPase was studied in rela tion to in vitro exposure of lead; these studies suggest a non-competitive type of inhibition. (C) 2000 Elsevier Science Inc, All rights reserved.