Impact of PF-4 on the cleavage of SP by purified chymase and CathG. SP (10 μM) was incubated with the same enzyme concentrations as used previously for CTAP-III processing of either 250 ng/mL chymase (left panels) or 500 ng/mL CathG (right panels) for 0, 30, and 120 minutes in the absence (solid line) and in the presence (broken line) of PF-4 (4 μM) in processing buffer at 37°C. SP and its cleavage products were separated by reverse-phase HPLC using a linear acetonitrile gradient in 0.1% TFA (dashed line). Peptides as detected by their absorbance at 214 nm at retention times of 20.4 minutes, 13.7 minutes, 15.4 minutes, and 17.1 minutes were analyzed by ESI-FT-MS and identified by their respective mass of 1363 amu, 901 amu, 466 amu, and 1048 amu as full-size SP (SP[1-11], calculated mass of oxidized form, 1363 amu) and fragments SP[1-7] (901 amu), SP[8-11] (467 amu), and SP[1-8] (1046 amu). One representative experiment of 3 is shown.