Thiophilic interaction chromatography of Alzheimer's β‐amyloid peptides

Alzheimer's disease is characterized by a progressive formation of senile plaques in the brain, the major constituent of which is β‐amyloid (Aβ) peptide, a proteolytic product of the transmembrane β‐amyloid precursor protein (APP). Prior to the measurement of levels of the Aβ peptide for diagnostic purposes, this peptide must be isolated from the myriad of proteins resident in the human serum. Thiophilic interaction chromatography is an effective method for the isolation of proteins and peptides containing clusters of aromatic residues such as tryptophan, phenylalanine and tyrosine. The purpose of the present study was to develop a protocol for binding and recovery of Aβ peptides (1–38), (1–40) and (1–42) to T‐gels by varying T‐gel type and elution conditions such as the salt concentration and type of eluent. We established the minimal salt concentration necessary for the binding of the Aβ(1–40) peptide to the 3S‐gel; binding at that concentration was subsequently compared with that of model proteins, lysozyme and α‐chymotrypsin and this methodology was extended to 2S‐gels and PyS. β‐Amyloid peptide (1–40) showed a remarkably strong affinity for all three types of T‐gels in comparison to lysozyme and α‐chymotrypsin and was found to bind best to 2S‐gel.