Adsorption studies of tritium-labeled peptides on polystyrene surfaces

In this study, three presentation formats of an epitope peptide (hepta-pept ide), derived from the human chorionic gonadotropin amino acid sequence, we re compared for adsorption to the polystyrene wells of a microELISA plate. The peptides had either a free N-terminus, an Ata-group or a linear (Lys)(7 )-extension at the N-terminal. In order to measure the adsorption propertie s, all peptides were tritiated by synthesizing an additional H-3 - labeled glycyl residue to the N-terminus of their peptide sequence. Over a broad ra nge of peptide concentrations used as coat solution, extension of the pepti de by an Ata-group consistently increased adsorption by a factor of 1.5 to 3 compared to the free parent peptide. Of the three peptides studied, the A ta-peptide showed the highest surface coverage of 0.6 mg/m(2) when 1.0 mmol /l was offered as the concentration of peptide in the coating solution. The highest surface coverage observed for the parent peptide was 0.4 mg/m(2) ( at 1.5 mmol/l). The lysyl (K-7) peptide showed a maximum plateau value of 0 .2 mg/m(2), and therefore the lysyl (K-7) extension reduced the peptide sur face coverage at relatively high coat concentrations (above 0.1 mmol/l) com pared to the parent peptide. At lower input concentrations (below 0.1 mu mo l/l), however, the packing density of the lysyl (K-7) peptide was up to 25 times higher when compared to the other two peptide analogs. We conclude th at better adsorption as well as improved antibody binding activity and (fun ctional) affinity could explain the higher reactivity observed in ELISA pro cedures when peptides are N-terminally extended by an Ata-group or lysyl (K -7) extension. (C) 1998 Elsevier Science B.V. All rights reserved.