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© 1998 Oxford University Press
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Plasma and Blood Lead in Humans: Capacity-Limited Binding to
-Aminolevulinic Acid Dehydratase and Other Lead-Binding Components1


*Department of Occupational and Environmental Medicine, Lund University SE-221 85 Lund, Sweden
Department of Occupational Diseases, St. Petersburg State Medical Academy St. Petersburg, Russia
Received September 29, 1997; accepted July 6, 1998
In 42 lead-exposed workers (22 male and 20 female), we found a close nonlinear relation between blood and plasma lead concentrations, determined by inductively coupled plasma mass spectrometry (ICP-MS). The concentration medians and ranges were lead in whole blood, 270 (97 to 950) µg/L and lead in plasma, 1.1 (0.2 to 13) µg/L. Proteins from lysed erythrocytes were studied by gel chromatography with ICP-MS detection. We then found capacity-limited binding for lead to
-aminolevulinic acid dehydratase (ALAD), as well as to two other components (with apparent molecular masses of 45 and <10 kDa, respectively). The strongest affinity for lead was indicated for ALAD (3581% of the lead in blood) and could be described by a capacity of 850 µg/L and a dissociation constant of 1.5 µg/L. The 45-kDa protein carried 1226% of the blood lead, and the <10-kDa component less than 1%. A model based on these three components, plus a fourth one for unrecovered lead (245%), is proposed. No binding of lead to hemoglobin was found. There was an association between zinc and lead in whole blood; however, zinc did not significantly affect the lead distribution in erythrocytes.
Key Words: lead; blood; plasma;
-aminolevulinic acid dehydratase, ALAD; proteins; model; lead-binding proteins.
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