A sensitive and specific enzyme-linked immunosorbent assay for methionine enkephalin sulphoxide.

An enzyme-linked immunosorbent assay (ELISA) for the sulphoxide derivative of the opioid peptide methionine enkephalin (MOE) was developed and found to be sensitive and highly specific. Methionine enkephalin itself showed only low cross-reactivity (1.8%) in the assay while leucine enkephalin and the endorphins showed cross-reactivity no higher than 0.6%. Given the ease of application, low cost and stable nature of the label, this technique is a useful alternative to existing radioimmunoassays for the peptide.