Arsenite binding to synthetic peptides: The effect of increasing length between two cysteines

We utilized radioactive 73 As‐labeled arsenite and vacuum filtration methodology to determine the binding affinity of arsenite to eight synthetic peptides ranging from 13 to 24 amino acids long and containing one or two cysteines separated by 0–17 intervening amino acids. Six of the eight peptides were highly similar in amino acid sequence and were based on cysteine containing regions of the hormone‐binding site of the human estrogen receptor‐alpha (e.g., the sequence of peptide 28 is LEGAWCGKGVEGTEHLYSMKCKNV). The peptides with 0–14 intervening amino acids between two cysteines bound arsenite with K d values of 2.7–20.1 uM and with B max values from 36 to 103 nmol/mg protein (from 0.083 to 0.19 nmol/nmol of protein). Thus, increasing the number of intervening amino acids from 0 to 14 made very little difference in the observed K d values for arsenite, a surprising finding. Therefore, these peptides are flexible in solution and effectively contain a dithiol high affinity binding site for arsenite. Peptide 17 with two C separated by 19 amino acids bound arsenite with a K d of 123 uM and a B max of 41.8 nmol/mg. The monothiol peptide 19 bound arsenite with a K d of 124 uM and a B max of 26 nmol/mg protein. All experi‐ mental binding curves fit well to a one site binding model. © 2006 Wiley Periodicals, Inc. * This article is a U.S. Government work and, as such, is in the public domain of the United States of America. J Biochem Mol Toxicol 20:35–38, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20112