The thiol enzyme from rat spleen that produces bradykinin potentiating peptide from rat plasma

We have focused our studies on a thiol-dependent enzyme of 37 kilodaltons (kDa) that produces a bradykinin (BK) potentiating peptide. The molecular mass of the peptide was estimated to be around 750 Da and its amino acid composition was Pro4 Gly2 Leu1 Ser1 with a proline and a serine at the N- and C-terminals, respectively. Biological activity was assayed by means of uterus contraction. The enzyme differs from Cathepsin L or B by virtue of its immunological reactivity and enzyme kinetics. The inhibitors used were leupeptin, antipain, E-64 and chymostatin in order of effectiveness. The low molecular SH reagents also diminished the enzyme activity. Among the metal ions tested, Cu2+ and Zn2+ inhibited the reaction.