IDENTIFICATION OF TARGETING PROTEINASE FOR RAT ALPHA(1)-MACROGLOBULININ-VIVO - MAST-CELL TRYPTASE IS A MAJOR COMPONENT OF THE ALPHA(1)-MACROGLOBULIN-PROTEINASE COMPLEX ENDOCYTOSED INTO RAT-LIVER LYSOSOMES

The alpha(1)-macroglobulin-proteinase complex endocytosed into rat liv er lysosomes was purified by a series of column chromatographic steps on concanavalin A-Sepharose, Sephacryl S-300, DEAE-cellulose and TSK g el DEAE-5PW columns. The complex contained no detectable alpha(2)-macr oglobulin. Studies on the substrate specificity indicated that the com plex had tryptase-like activities towards various synthetic substrates , but no elastase, chymotrypsin, cathepsin-B and cathepsin-L activitie s. The proteinase activity was completely inhibited by di-isopropyl fl uorophosphate, leupeptin and antipain, indicating that the proteinase bound to alpha(1)-macroglobulin is a serine proteinase. Two protein ba nds (62 and 59 kDa) of the complex were labelled with [H-3]di-isopropy l fluorophosphate and both bands cross-reacted with anti-(mast-cell tr yptase)antibody. These results suggest that mast-cell tryptase is a ma jor targeting proteinase for alpha 1(-)macroglobulin in vivo. The main alpha-macroglobulin-proteinase complex in the adjuvant-treated rats w as also the alpha(1)-macroglobulin-tryptase complex, even though the p lasma level of alpha(2)-macroglobulin was elevated.