Use of [75Se]selenomethionine in immunoglobulin biosynthetic studies.

The gamma-emitting amino acid analog, [75Se]selenomethionine, has been used as a biosynthetic label for immunoglobulins secreted by plasmacytomas in tissue culture. The secreted products are structurally intact with respect to their antibody combining sites and their class and allotype antigenic specificities. A component of [75Se]selenomethionine preparations was found to bind to fetal calf serum proteins, in a manner releasable by mercaptoethanol, but not by sodium dodecyl sulfate (SDS) and urea. Methods for circumventing the problems caused by this binding are described.