Figure 3. Identification of the furin cleavage site.

Purified recombinant Spn1 (720 nM) was incubated (60 min at 30 °C) in the presence of furin (98 nM) followed by MALDI–TOF-MS analysis. The signal at m/z=4918.29 indicates cleavage between Arg³⁶⁴ and Ser³⁶⁵ in the RSL (A). The signal was not observed in the mass spectrum of the uncleaved inhibitor (B).