A novel method in enzyme immunoassay: maleimide derivative of hapten for enzyme coupling.

Meta-maleimidobenzoyl derivative of L-thyroxine methyl ester (MBTM) was synthesized and coupled to beta-galactosidase at molar ratio of over 5 to 1. More than 97% of the enzyme was found to be labeled with MBTM. A thyroxine enzyme immunoassay was carried out with sensitivity in 0-10 microgram/100 ml range.