Fig. (3) Protease specificity determination using tumor extract from S180 sarcomas A: SDS-PAGE analysis for the tumor extract. B: Mass spectra of the biotin-labeled substrates digested with tumor extracts showing the fragments detected after cleavage of C-terminal Lys, Phe, and Tyr. C: Mass spectra of the biotin-labeled substrates digested with tumor extracts inactivated by boiling for 10 min.