Toxicity induced by Hg2+ on choline acetyltransferase activity from E. electricus (L.) electrocytes: the protective effect of 2,3 dimercapto-propanol (BAL).
BACKGROUND
The effect of mercury (Hg(2+)) on the activity of choline acetyltransferase (ChAT) from electrocytes of Electrophorus electricus (L.) was studied due to the importance of this enzyme and acetylcholine in many neurochemical functions such as arousal, learning, and memory.


METHODS
Mercury, which has affinity to thiol groups, acted as a potent inhibitor of ChAT, which was obtained by differential centrifugation and ammonium sulfate precipitation, at 80%, from the main electric organ homogenate.


RESULTS
Mercury inhibition presents different kinetic behaviors for both enzyme substrates: noncompetitive to choline and of mixed type to AcCoA, with inhibition constants on the order of 0.5 to 1.0 microM. The enzyme activity was recovered using 2,3 dimercapto-propanol (BAL), a well-known chelate for sulphydryl groups and metals, which acted as a protecting agent and was able to revert the Hg(2+) inhibition at a concentration of 10 (-6) M. After treatment with this metal and in the presence of 2,3 dimercapto-propanol, 70% of the enzyme activity was recovered for AcCoA and 80% for choline.


CONCLUSIONS
The observed inhibition is likely due to direct protein interaction, because the addition of BAL reversed the effects of HgCl(2) on ChAT activity. The results cast new light on the mechanisms of mercurial neurotoxicity.
Nunes-Tavares
Nilson
N
Laboratório de Físico-Química Biológica Aída Hassón-Voloch, Instituto de Biofísica Carlos Chagas Filho, Universidade do Brasil-UFRJ, Centro de Ciencias da Saúde, Rio de Janeiro, RJ 21949-590, Brasil.
Valverde
Rafael Hospodar Felippe
RH
Araújo
Glauce Maria Nunes
GM
Hassón-Voloch
Aida
A
D000818:Animals; D002614:Chelating Agents / Q000627:therapeutic use*; D002795:Choline O-Acetyltransferase / Q000378:metabolism*; D004112:Dimercaprol / Q000627:therapeutic use*; D004557:Electric Organ / Q000201:enzymology*; D004593:Electrophorus / Q000502:physiology*; D007700:Kinetics; D008630:Mercury Poisoning / Q000201:enzymology* / Q000517:prevention & control*
D002614:Chelating Agents; D004112:Dimercaprol; D002795:Choline O-Acetyltransferase