Assessment of HRR/PRR release in serum-purified rabbit HRG. (A) SDS-PAGE analysis of rabbit HRG following treatment with or without plasmin and DTT. The HRR/PRR band is highlighted in the box and only appears under reducing conditions. (B) MS/MS analysis of the HRR/PRR band excised from the gel. Peptide sequences giving a confidence of 99% are in bold, and those with a 74% confidence in italics. The predicted sequence of the HRR/PRR plasmin cleavage product is highlighted in gray. NCBI accession number: XP_002716393. (C) Schematic showing release of HRR/PRR following both plasmin cleavage and reduction of the Cys185-Cys407 bond of HRG by GSH. The second interdomain disulfide bond between Cys6-Cys497 remains intact holding the remaining protein domains together.