EVIDENCE FOR A MAJOR STRONG BINDING SITE FOR TETRACHLOROSALICYLANILIDE ON HUMAN SERUM ALBUMIN

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Abstract
Abstract— Solutions of human serum albumin(HSA) monomer were irradiated with UV light(360 nm) in the presence of [14C]‐3,3.4′S‐tetrachlorosalicylanilide([14C]‐T4CS).The [14C]‐T4 CS‐labeiled HSA was cleaved by cyanogen bromide and separated into two fractions. These fractions were reduced carboxymethylated and separated into their seven characteristic peptides and monitored for radioactivity. Tetrachlorosalicylanilide was found to bind mainly to one region of the sequence of HSA and this covalent binding site was located in residues 124 (Cys) to 298 (Met) of the molecule. The binding of 3,5‐dichlorosalicylamido‐4‐(2,2,6.6‐tetramethylpiperidine‐l‐oxyl (DCS‐TEMPO),a spin‐label analogue of T4CS, to HSA was studied by electron spin resonance spectroscopy. In the absence of UV light. DCS‐TEMPO bound non‐covalently (k = 6.1 times 106M1) to one major binding site on HSA. These results are evidence for the existence of a major strong binding site for the photochemical binding of T4CS to HSA.

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