Characterization of Ca2+-ATPase activity in gill microsomes of freshwater mussel, Lamellidens marginalis (Lamarck) and heavy metal modulations

Freshwater mussel Lamellidens marginalis showed a Ca2+-stimulated ATPase activity in the microsomal fraction of gill. Mg2+ was also found to be an activating cation for this ATPase enzyme. Ca2+ ATPase showed maximal activity at 40 degrees C and between pH 7.5-8.0. Substrate specificity of Ca2+ ATPase was highest with ATP, followed by GTP and other trinucleotides such as UTP, CTP and ADP also showed some amount of hydrolysis. Ca2+ ATPase showed slight inhibition with ruthenium red and sodium vanadate and is insensitive to sodium azide, ouabain, oligomycin B and phenylalanine. Heavy metals like Hg-2+ ,Hg- CU2+ and Zn2+ showed 50% inhibition of Ca2+ ATPase activity at concentrations of 0.25 mM, 0.5 mM and I mM, respectively whereas Cd2+ and Ni2+ showed 39% and 28% inhibition of enzyme activity at 1 mM concentrations. (c) 2007 Elsevier B.V. All rights reserved.