Interaction of Cd2+ with the calmodulin-activated (Ca2+ + Mg2+)-ATPase activity of human erythrocyte ghosts.
Treatment of erythrocyte ghosts with micromolar concentrations of Cd2+ results in a noncompetitive inhibition of the calmodulin-dependent (Ca2+ + Mg2+)-ATPase activity. Higher concentrations of Cd2+ are required for inhibition of the (Ca2+ + Mg2+)-ATPase activity of calmodulin-depleted ghosts. The interaction of Cd2+ is time-dependent with an apparent rate constant around 0.12/min. The inhibition is relieved by addition of EGTA with a rate constant around 0.15/min. If Cd2+ is allowed to interact with calmodulin prior to the association of the protein with the ghosts, the inhibition is mainly competitive. The results suggest that the inhibitory effect caused by Cd2+ is due to an interaction with calmodulin. The slow interaction of Cd2+ suggests that calmodulin bound to the (Ca2+ + Mg2+)-ATPase is inaccessible to Cd2+.
Akerman
K E
KE
Honkaniemi
J
J
Scott
I G
IG
Andersson
L C
LC
D017301:Ca(2+) Mg(2+)-ATPase; D002104:Cadmium / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors* / Q000097:blood; D002147:Calmodulin / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004910:Erythrocyte Membrane / Q000201:enzymology*; D006801:Humans; D066298:In Vitro Techniques
D002147:Calmodulin; D002104:Cadmium; D004533:Egtazic Acid; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases