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 kilodalt ons (kDa) that produces a bradykinin (BK) potentiating peptide. The mo lecular mass of the peptide was estimated to be around 750 Da and its amino acid composition was Pro(4)Gly(2) Leu(1) Ser(1) with a proline a nd a serine at the N- and C-terminals, respectively. Biological activi ty 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 chym ostatin 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.