Fig. 6
Specific solid-phase radioimmunoassay for the P18C5 mAb. The P18C5 mAb was used to generate a reliable and sensitive solid-phase RIA for detecting the structural α-amidated isoform of the valine residue in synthetic peptide and non-peptide antigens. As shown, the P18C5 mAb was highly sensitive in detecting the VAL-CONH2 residue in metorphamide/adrenorphin, BSA-VAL-CONH2 and Tyr-Gly2-4-Val-CONH2 antigens within the tested concentration range, displaying IC50 values of 64.6 ± 9.7 fmol/well, 111.97 ± 32.4 fmol/well, and 154.4 ± 48.3 fmol/well, respectively. However, no cross-reactivity (IC50 = ND) was detected against antigens expressing the Val-COO− residue in Tyr-Gly2-4-Val-COO− or RGDV-COO−, including mastoparan X, within the range of competitive antigen concentrations (0.1 fmol–10 nmol) tested in the assay (see text for additional details)