Evidence of hemoglobin binding to arsenic as a basis for the accumulation of arsenic in rat blood.
Four trivalent arsenic species, inorganic arsenite (iAs(III)), monomethylarsonous acid (MMA(III)), dimethylarsinous acid (DMA(III)), and phenylarsine oxide (PhAs(III)O), have shown increasing binding affinity with the hemoglobin (Hb) of rats and humans. The binding stoichiometry was consistent with the number of reactive cysteine residues in the alpha and beta chains of Hb. Comparing the binding affinity of rat Hb and human Hb for the same trivalent arsenic species, rat Hb was 3-16 times stronger than human Hb as demonstrated by their apparent binding constants. Comparative experiments involving incubation of human and rat red blood cells (RBC) with iAs(III), MMA(III), and DMA(III) showed that 15-30-fold more arsenic species were bound to the Hb of rat RBC than that of human RBC. In vivo experiments using rats fed with an arsenic-supplemented diet showed that arsenic in RBC of the rats was predominantly found in the protein-bound form. Further characterization by nanoelectrospray mass spectrometry of the arsenic species in the RBC of these rats confirmed that most arsenic was bound to the alpha chain of Hb. Taken together, these results suggest that the stronger binding affinity of these arsenic species to rat Hb is responsible for the accumulation of arsenic in rat blood. The results provide a chemical basis to explain the previously observed intriguing difference in the retention of arsenic in the human and the rat. The techniques and approaches described can be applied to the studies of arsenic interactions with other functional proteins.
Lu
Meiling
M
Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G3, Canada.
Wang
Hailin
H
Li
Xing-Fang
XF
Lu
Xiufen
X
Cullen
William R
WR
Arnold
Lora L
LL
Cohen
Samuel M
SM
Le
X Chris
XC
D000818:Animals; D001151:Arsenic / Q000097:blood* / Q000378:metabolism; D001152:Arsenicals / Q000097:blood; D002101:Cacodylic Acid / Q000031:analogs & derivatives* / Q000633:toxicity; D005260:Female; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D009942:Organometallic Compounds / Q000633:toxicity; D051381:Rats
D001152:Arsenicals; D006454:Hemoglobins; D009942:Organometallic Compounds; C472511:dimethylarsinous acid; C406082:monomethylarsonous acid; D002101:Cacodylic Acid; D001151:Arsenic