Effect of lead on the erythrocyte (Ca2+,Mg2+)-ATPase activity Calmodulin involvement (original) (raw)
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British Journal of Haematology, 1981
Summary. In normal erythrocytes, a membrane‐bound (Ca2++ Mg2+)‐ATPase is stimulated by a soluble activator, calmodulin. Since cells containing Hb S accumulate excessive Ca2+, the defect could lie in either the (Ca2++ Mg2+)‐ATPase or calmodulin. To decide between these two possibilities, we prepared (Ca2++ Mg2+)‐ATPase from erythrocytes of normal (AA), sickle cell trait (AS) and sickle cell disease (SS) individuals. Calmodulin was prepared from haemolysates from AA and SS erythrocytes. The enzyme prepared from SS ghosts had lower specific activity than that from AA membranes. Furthermore, calmodulin from either source did not stimulate the ATPase of SS erythrocytes. Enzyme from AS cells had specific activity similar to that of enzyme prepared from SS membranes. The enzymatic activity of a mixed cell population obtained from an SS patient 8 d following exchange‐transfusion was proportional to the per cent Hb A. These results indicate that calmodulin is unable to interact with the enzy...
Lead and calcium transport in human erythrocyte
Human & Experimental Toxicology, 1999
In this paper we report the lead (Pb) and calcium [Ca) uptake by erythrocyte ghosts. In both cases the transport was carried out by a passive transport system with two kinetic components (Michaelis-Menten and Hill). Pb and Ca were capable of inhibiting the transport of the other metal in a non-competitive way. Under hyperpolarization. the uptakes of Ca and Pb were enhanced and the Michaelis-Menten component prevailed. Both Ca and Pb I
Lead-induced changes in human erythrocytes and lymphocytes
Journal of Applied Toxicology, 2005
In the present work we studied, by chemiluminescence measurements, the influence of lead on the production of reactive oxygen species (ROS) in haemolysates obtained from human erythrocytes incubated in the presence of different concentrations of lead acetate. Moreover, we evaluated the modification of proteins and lipids in human erythrocyte and lymphocyte membranes by using the fluorescence probes N-(1-pyrene)maleimide (PM), laurdan and pyrene. No significant changes in chemiluminescence were detected for erythrocytes incubated with 1-10 µ µ µ µ µM lead acetate for 3 h at 37°C. By increasing the lead acetate concentration in cell suspensions up to 50 µ µ µ µ µM for the same incubation time, the percentage of chemiluminescence inhibition was ca. 20%. It was shown that, after incorporating fluorescence probes in the membrane lipid bilayer of erythrocytes and lymphocytes treated with 10 and/or 50 µ µ µ µ µM lead acetate, the total fluorescence intensity and the excimer to monomer intensity ratio of PM decreased and the generalized fluorescence polarization of laurdan decreased by 10-15%. The pyrene excimerization coefficient (κ κ κ κ κ ex ) increased by 20% (in comparison with a magnitude of κ κ κ κ κ ex for white membranes isolated from intact erythrocytes) with 6-10 µ µ µ µ µM lead acetate for 3 h at 37°C.
Inhibition of human erythrocyte ?-aminolevulinate dehydratase by lead
Internationales Archiv f�r Arbeitsmedizin, 1974
Results of in vivo and in vitro experiments indicate that the decrease of ~-aminolevulinate dehydratase (ALAD) in human erythroeytes measured under usual environmental and occupational exposure to lead (blood lead concentration < 120 Ixg per 100 ml) is a true reflection of the enzyme activity in vivo.
Lead and other metals can substitute for Ca2+ in calmodulin
Archive Fur Toxikologie, 1983
We have studied the interaction between some heavy metal ions, as compared with earth alkali ions, and calmodulin, a tissue protein which binds Ca 2+ and mediates some of its effects. 1. Calmodulin dependent phosphodiesterase was activated with Pb 2+, Ca 2+, Sr 2+, Ba 2 § and Cd 2 § (ECso about 0.8 ~tM). The maximal activation achieved decreases in the order given. Hg 2+, Sn 2+, Fe 2+, Cu 2+, Ni 2 § Bi 3+, and Sb 3+ up to 20 ~tM did not activate. 2. Pb 2+ can replace Ca 2+ with respect to the calmodulin-dependent phosphorylation of brain membranes. With high Pb 2+ concentrations, phosphorylation was inhibited. 3. Calmodulin binding to brain membranes was enhanced with concentrations below 10-4M in the following order: Pb 2+ _-> Ca 2+ ~ Sr 2+ > Cd 2+ > Mn 2+ > Ba 2+. In contrast Mg 2+, Hg 2+, Sn 2+, Fe z+, Ni 2+, Co 2+, and Cu 2+ 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: Pb 2+ -Ca 2+ > Mn 2+, Ba 2+, Cd 2+, Sr 2+.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1990
The Ca2(+)-ATPase of the erythrocyte plasma membrane can be activated by calmodulin, acidic phospholipids, limited proteolysis and self-association. Recently, it has been shown that different organic solvents increase both the Vmax and the Ca2+ affinity of the enzyme (Benaim, G. and De Meis, L. (1989) FEBS Lett. 244, 484-486). In this report the effects of calmodulin and dimethyl sulfoxide (20%, v/v) on the Ca2(+)-ATPase are compared. Dimethyl sulfoxide also elicits the appearance of the low-affinity binding site, which in this enzyme is strictly dependent on calmodulin. Dimethyl sulfoxide increases the Ca2+ affinity of the enzyme in a manner similar to that observed with the use of calmodulin and of acidic phospholipids. This was tested using both native and partially trypsinized ATPase. When activated by calmodulin the enzyme is inhibited by compound 48/80, trifluoperazine and calmidazolium. When activated by dimethyl sulfoxide the enzyme is still inhibited by calmidazolium but is no longer inhibited by either compound 48/80 or trifluoperazine. Activation of the ATPase promoted by either calmodulin or dimethyl sulfoxide is abolished when the Ca2+ concentration is raised from 10 microM to 2 mM. The effect of dimethyl sulfoxide is also abolished by 20 mM Pi. In the presence of 1 to 10 mM Ca2+ the ATPase catalyzes an ATP in equilibrium Pi exchange. The rate of exchange increases several fold when dimethyl sulfoxide is included in the assay medium.
Biochimica et Biophysica Acta (BBA) - Molecular Cell Research, 1985
Treatment of erythrocyte ghosts with micromolar concentrations of Cd 2+ results in a noncompetitive inhibition of the caimodulin-dependent (Ca 2 + + Mg 2 +).ATPase activity. Higher concentrations of Cd 2 + are required for inhibition of the (Ca 2 ++ Mg 2+)-ATPase activity of calmodulin-depleted ghosts. The interaction of Cd 2+ 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 Cd 2+ 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 Cd 2+ is due to an interaction with calmodulin. The slow interaction of Cd 2+ suggests that calmodulin bound to the (Ca2++ Mg 2+)-ATPase is inaccessible to Cd 2 +.