Inhibition of Esterases in the Marine GastropodLittorina littoreaExposed to Cadmium

Electrophoretic analysis ofLittorina littoreaesterases indicated the presence of a cathodal migration isoenzyme (EST-C), which was identified in extracts obtained from the gonad–digestive gland complex. A loss of EST-C enzyme activity was observed in individuals exposed to Cd2+. This loss of activity was complete in 86% of individuals dead by the action of Cd2+and in 68% of those individuals that survived Cd2+exposure. This difference was statistically significant.In vitroinhibition of esterases by different concentrations of Cd2+and Cu2+was studied in individuals not experimentally exposed to heavy metals, to determine whether EST-C inhibition was caused by direct binding of Cd2+to the esterase molecule or by Cd2+displacement of a metal ion from essential Cu2+- or Zn2+-containing proteins, which may then be responsible for the inhibition of esterase. Contrary to what happened when individuals were exposed to Cd2+, in thein vitroexperiment with Cd2+, inhibition of anodal but not cathodal systems was observed. At the same time, when Cu2+was used in thein vitroexperiment, both anodal and cathodal systems were inhibited. These results suggest that the inhibition of EST-C activity by Cd2+takes placein vivoand seems not to be due to the direct action of Cd2+on the molecule, but rather is a process in which transcriptional, posttranscriptional, and other inhibitory processes may be involved.