The ALA-D Activity Test in Lead-Exposed Grey-Mullet Mugil auratus

The effect of sublethal exposure of grey mullet Mugil auratus Risso to lead (82 d in 500 pg Pb I-') was recorded by means of A M -D activity and hemoglobin concentration decrease. Maximum ALA-D inhibition (about 40 96) occurred after the second week, but the lead accumulation in the blood still increased. The specific pH optimum (pH 6 . M . 2 ) , the optimal substrate concentration (4 mM A M ) and the routine temperature incubation (37 "C) in the testing procedure were determined. Cadmium, copper and mercury (10-7 to 10" M) added 'in vitro' produce significant inhibition of ALA-D, while lower concentrations of zinc (10-' to 10" M) slightly increase enzyme activity of unexposed mullets. Higher concentrations of zinc (10-5 to 104 M) strongly reactivate the inhibited AM-D of the mullets previously exposed to lead.