ISSN:
1432-0738
Keywords:
Calmodulin
;
Ca2+
;
Pb2+
;
Phosphodiesterase
;
Phosphorylation
;
Brain
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract We have studied the interaction between some heavy metal ions, as compared with earth alkali ions, and calmodulin, a tissue protein which binds Ca2+ and mediates some of its effects. 1. Calmodulin dependent phosphodiesterase was activated with Pb2+, Ca2+, Sr2+, Ba2+, and Cd2+ (EC50 about 0.8 μM). The maximal activation achieved decreases in the order given. Hg2+ Sn2+, Fe2+, Cu2+, Ni2+, Bi3+, and Sb3+ up to 20 μM did not activate. 2. Pb2+ can replace Ca2+ with respect to the calmodulin-dependent phosphorylation of brain membranes. With high Pb2+ concentrations, phosphorylation was inhibited. 3. Calmodulin binding to brain membranes was enhanced with concentrations below 10−4 M in the following order: Pb2+ ≧Ca2+ ∼ Sr2+ 〉 Cd2+ 〉 Mn2+ 〉 Ba2+. In contrast Mg2+, Hg2+, Sn2+, Fe2+, Ni2+, Co2+, and Cu2+ triggered, if at all, a non-saturable binding of calmodulin. 4. In the flow-dialysis, other ions competed with 45Ca2+ binding to calmodulin in the following order: Pb2+ ∼ Ca2+ 〉 Mn2+, Ba2+, Cd2+, Sr2+. Thus among the ions investigated Pb2+ is a fully potent substitute for Ca2+ in every calmodulin-dependent reaction investigated. Cd2+ is always much less potent. The earth alkali ions Sr2+ and Ba2+ take an intermediate position. It remains to be shown whether calmodulin is merely a storage site for Pb2+, or whether the resulting functional changes play a role in Pb2+ poisoning.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00277816
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