Protease nexin. Properties and a modified purification procedure

• Published in: The Journal of biological chemistry Vol. 260; no. 11; pp. 7029 - 7034
• Main Authors: Scott, R W, Bergman, B L, Bajpai, A, Hersh, R T, Rodriguez, H, Jones, B N, Barreda, C, Watts, S, Baker, J B
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 10.06.1985; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acids - analysis; Amyloid beta-Protein Precursor; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Carrier Proteins - metabolism; Enzymes and enzyme inhibitors; Fibroblasts - analysis; Fundamental and applied biological sciences. Psychology; Heparin - metabolism; Humans; Hydrolases; Kinetics; Mathematics; Molecular Weight; Protease Inhibitors - metabolism; Protease Nexins; Receptors, Cell Surface; Substrate Specificity; Thrombin - antagonists & inhibitors; Trypsin - metabolism; Human; Cell culture; Purification; Enzyme; Proteinase; Inhibitor; Serine proteinase; Fibroblast; Biological activity
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)88883-4

The present paper describes chemical and functional properties of protease nexin, a serine protease inhibitor released from cultured human fibroblasts. It is shown that protease nexin is actually synthesized by fibroblasts and represents about 1% of their secreted protein. Analysis of the amino acid composition of purified protease nexin indicates that it is evolutionarily related to antithrombin III and heparin cofactor II. Protease nexin contains approximately 6% carbohydrate, with 2.3% amino sugar, 1.1% neutral sugar, and 3.0% sialic acid. The Mr calculated from equilibrium sedimentation analysis is 43,000. Protease nexin is a broad specificity inhibitor of trypsin-like serine proteases. It reacts rapidly with trypsin (kassoc = 4.2 +/- 0.4 X 10(6) M-1 s-1), thrombin (kassoc = 6.0 +/- 1.3 X 10(5) M-1 s-1), urokinase (kassoc = 1.5 +/- 0.1 X 10(5) M-1 s-1), and plasmin (kassoc = 1.3 +/- 0.1 X 10(5) M-1 s-1), and slowly inhibits Factor Xa and the gamma subunit of nerve growth factor but does not inhibit chymotrypsin-like proteases or leukocyte elastase. In the presence of heparin, protease nexin inhibits thrombin at a nearly diffusion-controlled rate. Two heparin affinity classes of protease nexin can be detected. The present characterization pertains to the fraction of protease nexin having the higher affinity for heparin. The low affinity material, which is the minor fraction, is lost during purification.