A simple procedure for isolating microgram quantities of biologically active bikunin from human urine

Heavy chains of inter alpha inhibitor (IαI) inhibit the human complement system at early stages of the cascade

Inter alpha inhibitor (IαI) is an abundant serum protein consisting of three polypeptides: two heavy chains (HC1 and HC2) and bikunin, a broad-specificity Kunitz-type proteinase inhibitor. The complex is covalently held together by chondroitin sulfate but during inflammation IαI may interact with TNF-stimulated gene 6 protein (TSG-6), which supports transesterification of heavy chains to hyaluronan. Recently, IαI was shown to inhibit mouse complement in vivo and to protect from complement-mediated lung injury but the mechanism of such activity was not elucidated. Using human serum depleted from IαI, we found that IαI is not an essential human complement inhibitor as was reported for mice and that such serum has unaltered hemolytic activity. However, purified human IαI inhibited classical, lectin and alternative complement pathways in vitro when added in excess to human serum. The inhibitory activity was dependent on heavy chains but not bikunin and detected at the level of initiating molecules (MBL, properdin) in the lectin/alternative pathways or C4b in the classical pathway. Furthermore, IαI affected formation and assembly of the C1 complex and prevented assembly of the classical pathway C3-convertase. Presence and putative interactions with TSG-6 did not affect the ability of IαI to inhibit complement thus implicating IαI as a potentially important complement inhibitor once enriched onto hyaluronan moieties in the course of local inflammatory processes. In support of this, we found a correlation between IαI/HC-containing proteins and hemolytic activity of synovial fluid from patients suffering from rheumatoid arthritis.

A stable trypsin inhibitor from Chinese dull black soybeans with potentially exploitable activities

A dimeric 40-kDa Kunitz-type trypsin inhibitor was isolated from seeds of the Chinese black soybean Glycine max cv. ‘Dull Black’. The purification protocol comprised ion exchange chromatography on Q-Sepharose, SP-Sepharose, and Mono Q, and gel filtration on Superdex 75. The trypsin inhibitor inhibited chymotrypsin, albeit to a lesser extent than it inhibited trypsin. Its trypsin-inhibitory activity was unaffected after exposure to pH 1–14, or to temperatures up to 80 °C. The trypsin inhibitor was inhibited by dithiothreitol in a dose-dependent (from 2.5 to 50 mM) and a time-dependent (from 5 to 120 min) manner. Besides inhibiting serine proteases, the trypsin inhibitor demonstrated additional biological activities including stimulation of nitric oxide production by macrophages. It inhibited HIV-1 reverse transcriptase, cell-free translation and proliferation of liver cancer cells and breast cancer cells, with an IC₅₀ value 9.4, 14, 39 and 70 μM, respectively. However, it did not exhibit antifungal, antibacterial or mitogenic activity.

Purification and characterization of aprotinin from porcine lungs

Aprotinin, the most studied serine proteinase inhibitor, was isolated from porcine lung for the first time. The purified porcine aprotinin had an Mr value of approximately 7 kDa. It cross-reacted with polyclonal serum anti-commercial aprotinin. About 1 microg porcine aprotinin inhibited 6 microg trypsin whereas 1 microg commercial soybean inhibitor inhibited only 1 microg trypsin. The aprotinin gene was also isolated from porcine lung: the deduced amino acid sequence showed 74% identity to bovine aprotinin.