title: Cysteine-specific radioiodination of proteins with fluorescein maleimide.
abstract: A protocol is described for coupling of carrier-free iodine to protein sulfhydryl groups via fluorescein maleimide. 125I is first coupled to fluorescein maleimide in the presence of chloramine T. Iodination is stopped with sodium thiosulfate, and the iodine-substituted fluorescein maleimide is reacted with free cysteines of the protein. Excess label is then removed by gel-permeation chromatography. The procedure avoids exposition of the protein to oxidative conditions and does not require purification of the labeled carrier reagent. Suitability of the method for a given protein can be evaluated spectrophotometrically without employing radioactivity. It can be applied under denaturing conditions and may be particularly useful with mutant proteins carrying engineered single cysteine residues at sites that are not functionally critical.
authors.affiliation: Institute of Medical Microbiology, University of Mainz, Augustusplatz, D55101, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Palmer
authors.forename: M
authors.initials: M
authors.lastname: Buchkremer
authors.forename: A
authors.initials: A
authors.lastname: Valeva
authors.forename: S
authors.initials: S
authors.lastname: Bhakdi
mesh_terms: D001426:Bacterial Proteins; D002700:Chloramines / Q000737:chemistry; D002850:Chromatography, Gel; D015941:Complement Hemolytic Activity Assay; D003545:Cysteine / Q000737:chemistry*; D004912:Erythrocytes; D005452:Fluoresceins / Q000737:chemistry*; D007457:Iodine Radioisotopes / Q000032:analysis*; D011108:Polymers; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013053:Spectrophotometry; D013301:Streptolysins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D013885:Thiosulfates / Q000737:chemistry; D014105:Tosyl Compounds / Q000737:chemistry
chemical_list: D001426:Bacterial Proteins; D002700:Chloramines; D005452:Fluoresceins; D007457:Iodine Radioisotopes; D011108:Polymers; D011506:Proteins; D013301:Streptolysins; D013885:Thiosulfates; D014105:Tosyl Compounds; C016300:chloramine-T; C025964:streptolysin O; C037041:fluorescein 5-maleimide; C017717:sodium thiosulfate; D003545:Cysteine