Pulse chase analysis of antibody fragments in MAb 2G12 transgenic plant cells. Protoplasts from leaves of transgenic tobacco plants expressing the MAb 2G12 were washed and analysed by SDS-PAGE and western blotting (Panels C and D) or pulse-labelled for 1 hr and chased for the indicated periods of time (Panels A and B). Extracellular medium samples and homogenised cells were subjected to immunoprecipitation with Protein G/Protein A mix. Immunoprecipitated proteins were analyzed by SDS-PAGE and radiography. The asterisk corresponds to the fully assembled 2G12 antibody, while the lower case letters (a to i) indicate antibody fragments. Panels A and C were performed under non-reducing conditions, whereas samples in Panels B and D were reduced with the addition of 5% β-mercaptoethanol prior to boiling.