Concentration dependence of trypsin digestion of Glu-Pg. Glu-Pg was reduced and alkylated and either untreated (0) or digested with the indicated weight ratio of trypsin to Glu-Pg for 1 hour and coated onto wells of microtiter plates as described in “Methods.” Reactivity with mAb 51 (□; A), mAb 109 (□; B) and mAb 116 (□; C) was determined by ELISA as described in “Epitope determination: ELISA analysis of trypsin digests of Pg” and compared with the isotype control, MOPC21 (■ in all panels). *The trypsin:Glu-Pg ratio selected for study of each mAb.