PARENT SESSION
5B The use of biomarkers for assessing ecosystem damage
9:00 AM to 7:00 PM, Wednesday, 09 May 2001

(W/EH127) Lead effect on -aminolevulinic acid dehydratase in Halobatrachus didactylus (Schneider, 1801).

Campana, Olivia¹, Sarasquete, Carmen¹, Blasco, Julián¹, ¹

ABSTRACT- The -aminolevulinic acid dehydratase (ALA-D) (EC 4.2.1.24) is the second enzyme of the heme-biosynthesis pathway and catalyses the condensation of two molecules of -aminolevulinate to form the precursor of tetrapyrrolic compounds, porphobilinogen (PGB) (Gibson et al., 1955; Cheh and Neilands, 1973). An important characteristic of this enzyme is the essential role of sulfhydryl groups in its activity. Therefore ALA-D is inhibited by sulfhydryl reagents such as p-chloromercuribenzoate, N-ethylmaleimide, iodoacetate (Barreiro, 1967; Battle et al., 1967) and by some heavy metals (Rodrigues et al., 1989). In particular, this cytosolic enzyme is well known for its sensitivity to Pb2+ inhibition in human red blood cells, ALA-D activity being used as biomarker of Pb exposure in humans (Granick et al., 1972; Anderson et al., 1979). This research is part of a study in which ecotoxicological lead effects on Halobatrachus didactylus are investigated. The organisms were injected with a saline solution of lead (100 mg Pb/L in 0.9% NaCl in a ratio of 1 mL of solution for 100 g of fresh weight) and samples were collected at different times during the experiments. The biochemical effect of lead on -aminolevulinic acid dehydratase in blood and liver was examined and compared in order to evaluate the sensitivity of this enzyme to lead exposure in Halobatrachus didactylus. In addition to the ALA-D activity determination an histological and histochemical approach was carried out to complete the information about the lead effect on metabolism. The data presented may contribute to better evaluation of the use of ALA-D activity as indicator of lead pollution in fish.

Key words: lead, -aminolevulinic acid dehydratase , Halobatrachus didactylus, pollution