Inhibition kinetics of human serum butyrylcholinesterase by Cd2+, Zn2+ and Al3+: comparison of the effects of metal ions on cholinesterases.
Butyrylcholinesterase (BChE, EC 3.1.1.8) has been purified about 6600-fold from human serum with a procedure including ammonium sulfate fractionation (55-70%) with acid step at pH 4.5 and procainamide-Sepharose 4B affinity chromatography. The purified enzyme exhibited negative cooperativity with respect to butyrylthiocholine (BTCh) binding at pH 7.5. Ks was found to be 0.128 +/- 0.012 mM. Inhibition kinetics of the enzyme by Cd2+, Zn2+ and Al3+ were studied in detail. The 1/v vs 1/[BTCh] plots in the absence (control plot) and in the presence of different concentrations of cations intersected above 1/[BTCh]-axis. The data were analyzed by means of a nonlinear curve fitting program. The results demonstrated that all of the three cations are the linear mixed-type inhibitors of BChE. Ca2+ and Mg2+ had no effect on the enzyme activity in the experimental conditions. But when the enzyme was inhibited by 0.5 mM Cd2+ or Zn2+, Ca2+ and Mg2+ partially reactivated the inhibited allosteric form of BChE. Results were compared with data obtained from brain BChE purified from sheep.
Sarkarati
B
B
Department of Biochemistry, Faculty of Medicine, Hacettepe University, Ankara, Turkey.
Cokuğraş
A N
AN
Tezcan
E F
EF
D000495:Allosteric Site; D000535:Aluminum / Q000494:pharmacology*; D002091:Butyrylcholinesterase / Q000097:blood*; D002104:Cadmium / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology; D002800:Cholinesterase Inhibitors / Q000494:pharmacology*; D004793:Enzyme Reactivators / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D015032:Zinc / Q000494:pharmacology*
D002800:Cholinesterase Inhibitors; D004793:Enzyme Reactivators; D002104:Cadmium; D000535:Aluminum; D002091:Butyrylcholinesterase; D008274:Magnesium; D015032:Zinc; D002118:Calcium