Enzymatic properties of human leukocyte cathepsin G and its complex with a2-macroglobulin

Leukocyte cathepsin G (CLP) and elastase (ELP) from human blood were partially purified, and enzymatic properties of CLP and a2-macroglobulin-CLP complex (a2M-CLP) were studied in comparison with those of ELP and a2M-ELP. Furthermore, some synthetic substrates and synthetic reversible inhibitors for CLP were newly synthesized and specificities for CLP were compared with those of a-chymotrysin. The results obtained were as follows. 1) CLP was extracted with 2M NaC104 for 1hr, and delipidated by CC14 after dialysis in tris-HCl buffer (0.1M, pH 7.5) containing 0.5 M NaCl. Then, CLP was partially purified by Ultrogel AcA 44 gel chromatography. 2) The amidolytic activity of CLP increased with the addition of NaCl, KC1, MgCl2 and CaCl2 as was that of ELP, while the addition of NaC104, KSCN and KI enhanced the activity of ELP, but inactivated that of CLP. 3) The amidolytic activity of CLP or a2M-CLP was reduced with the addition of dimethyl sulfoxide in the reaction mixture, whereas that of ELP or a2M-ELP increased. 4) Kinetic parameters of Suc-Ile-Pro-Phe-pNA synthesized by the authors