Abstract
The physical and chemical properties of fluorescein isothiocyanate- and dansylchloridelabeled immunoglobulins were investigated. A marked change in solubility after labeling was noted. Depending on the time and on the type of fluorescent labeling rabbit and bovine immunoglobulin G showed different tendencies for precipitate formation. Increasing the molar fluorescein-protein ratio as well as lowering the pH of the conjugate solutions caused pronounced insolubilization. An increase in the NaCl concentration up to 0.5 M had no significant effect on precipitate formation. A simple method for the elimination of nonspecific staining is given. The method is based on the fact that overlabeled components of fluorescein isothiocyanate conjugates tend to precipitate; this can be initiated and furthered by lowering the pH of the conjugate solution.