抄録
A micro-scale method for the conjugation of affinity-purified Fab' to β-D-galactosidase from Escherichia coli is described. Rabbit anti-human chorionic gonadotropin serum (0.2 ml) was digested with pepsin to convert IgG to F(ab')2 and applied to a column of human chorionic gonadotropin-Sepharose 4 B, followed by elution at pH 2.5. The affinity-purified anti-human chorionic gonadotropin F (ab')2 was mixed with non-specific goat F (ab')2 (0.5mg) as a carrier, reduced with 2-mercaptoethylamine to split F (ab')2 to Fab' and conjugated to β-D-galactosidase using N, N'-o-phenylenedimaleimide. The affinity-purified rabbit anti-human chorionic gonadotropin Fab'-β-D-galactosidase conjugate was separated from non-specific goat Fab'-β-D-galactosidase conjugate and unconjugated β-D-galactosidase by affinity chromatography on a column of goat (anti-rabbit IgG) IgG-Sepharose 4 B using 4M urea. The amount of the affinity-purified conjugate obtained was 56-69 pg. The detection limit of human chorionic gonadotropin by a sandwich enzyme immunoassay technique was improved 30-fold by using the affinity-purified conjugate as compared with that before affinity-purification.
This method is applicable to the conjugation with alkaline phosphatase from calf intestine and probably also other enzymes which are stable in 4M urea.
