Abstract
Enzyme inhibition owing to cadmium (Cd) accumulation in the soluble high molecular weight fraction (HMF) of the liver from rainbow trout was investigated by measuring the inhibition of aminolevulinate dehydratase (ALAD). Factors affecting ALAD, which reacts specifically to metal, were examined before measuring ALAD activity. Although enzyme inhibition by Cd in the HMF was confirmed in the excretion 2 (E2) group fed Chinese parsley (CP), it was weaker than that in the excretion 1 (E1, control) group, probably due to the chelation of Cd by some substances contained in CP. Based on the absorption spectrum, the proportion of Cd bound to cysteine thiol radicals in the HMF of the E2 group was greater than that of E1. The HMF might detoxify harmful metals to some extent because it contains relatively higher levels of cysteine residues than metallothionein (MT) and shows comparatively weak enzyme inhibition. The results of the present study demonstrated that, in addition to MT, HMF is involved in the detoxification of harmful heavy metals in fish.
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