Lead-Binding Proteins : A Review

Abstract EN

Lead-binding proteins are a series of low molecular weight proteins, analogous to metallothionein, which segregate lead in a nontoxic form in several organs (kidney, brain, lung, liver, erythrocyte).

Whether the lead-binding proteins in every organ are identical or different remains to be determined.

In the erythrocyte, delta-aminolevulinic acid dehydratase (ALAD) isoforms have commanded the greatest attention as proteins and enzymes that are both inhibitable and inducible by lead.

ALAD-2, although it binds lead to a greater degree than ALAD-1, appears to bind lead in a less toxic form.

What may be of greater significance is that a low molecular weight lead-binding protein, approximately 10 kDa, appears in the erythrocyte once blood lead exceeds 39 μg/dL and eventually surpasses the lead-binding capacity of ALAD.

In brain and kidney of environmentally exposed humans and animals, a cytoplasmic lead-binding protein has been identified as thymosin β4, a 5 kDa protein.

In kidney, but not brain, another lead-binding protein has been identified as acyl-CoA binding protein, a 9 kDa protein.

Each of these proteins, when coincubated with liver ALAD and titrated with lead, diminishes the inhibition of ALAD by lead, verifying their ability to segregate lead in a nontoxic form.