Adsorption characteristics of bovine serum albumin and its peptide fragments on a stainless steel surface

Adsorption characteristics of peptide fragments prepared by lysyl endopeptidase treatment of bovine serum albumin (BSA) were studied in comparison with those of BSA itself using stainless steel particles (type 316L) as a substrate surface. BSA was adsorbed onto the stainless steel surface remarkably at acidic pHs but scarcely at alkaline pHs. The peptide fragments were also scarcely adsorbed at alkaline pHs. At acidic pHs, however, the affinity toward the stainless steel surface depended on the type of peptide fragment; several types of the peptide fragments, relatively rich in acidic amino acid residues, such as DLGEEHFK (residues 13-20) and DAIPEDLPPLTADFAEDK (residues 295-312), were considerably adsorbed onto the stainless steel surface at acidic pHs. Similarly to BSA, the adsorption isotherms of those two types of peptide fragments showed very high affinities toward the stainless steel surface at pH 3 resulting in irreversible adsorption. Adsorption experiments for their synthetic analogues showed that the acidic amino acid residues were essential for the adsorption at pH 3. Furthermore FT-IR analysis suggested that the carboxyl groups of these acidic amino acid residues on the stainless steel surface were dissociated and hence had electrostatic interaction with the stainless steel surface. Thus the importance of carboxyl groups in the adsorption of peptide fragments on the stainless steel surface at acidic pHs was indicated. Close similarity of adsorption behaviors at acidic pHs found between BSA and those peptide fragments suggests that the acidic amino acid residues of the corresponding segments of a BSA molecule make a major contribution to the adsorption at acidic pHs. However, when those adsorbed at pH 3 were treated with 0.02 N NaOH, complete removal was observed for the peptide fragments but not for BSA.