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Effects of lead and pesticides on δ‐aminolevulinic acid dehydratase of ring doves (Streptopelia risoria)
Author(s) -
Scheuhammer A. M.,
Wilson L. K.
Publication year - 1990
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1002/etc.5620091107
Subject(s) - chemistry , kidney , in vivo , dithiothreitol , pesticide , carbaryl , in vitro , dehydratase , biochemistry , whole blood , endocrinology , medicine , enzyme , biology , microbiology and biotechnology , agronomy
The effects of lead (Pb 2+ ) and various pesticides on δ‐aminolevulinic acid dehydratase (ALA‐d) in avian blood, liver and kidney were studied. In blood, virtually all of the ALA‐d activity was localized in the cellular fraction. Complete inhibition of RBC ALA‐d occurred at an in vitro Pb 2+ concentration of ∼10 μmol/g protein, with an IC50 of ∼0.9 μmol/g protein. Pesticides (carbaryl, carbofuran, chlorpyrifos, diazinon, dieldrin, fenitrothion, hexachlorobenzene) added to blood samples up to 10 mM in vitro had no inhibitory effect on ALA‐d, nor did the presence of pesticides greatly modify the response of ALA‐d to inhibition by increasing concentrations of Pb 2+ . Recovery of Pb‐inactivated RBC ALA‐d activity was accomplished by treatment of blood hemolysates with Zn 2+ and an SH‐reducing agent such as dithiothreitol (DTT). A combination of Zn 2+ (4 mM) and DTT (120 mM) was required to achieve complete recovery of Pb‐inhibited enzyme activity. Normal avian ALA‐d activity was greatest in blood, followed by liver, then kidney. Unlike blood hemolysates, liver and kidney homogenates contained a fraction of ALA‐d activity which was very resistant to inhibition by in vitro Pb 2+ . In vivo, hepatic ALA‐d was unaffected by Pb exposure (2.5 μg Pb 2+ /g body weight injected intraperitoneally), but renal ALA‐d was decreased as a result of greater deposition of Pb in kidney than in liver. Inhibition of ALA‐d in avian blood, particularly when expressed as a ratio of fully restored:nonrestored activity (activity ratio), is a highly specific, sensitive indicator of Pb exposure, deposition and corresponding enzyme inhibition in other target organs (kidney).