Figure 1.

Schematic of members of the IαI family in urine, blood, and tissues. Bikunin is found alone in the urine, whereas it is also found in the blood and tissues either alone or complexed with one HC, including HC1, HC2, HC3, or HC5. HC3 covalently bound to bikunin is called pre-α-inhibitor (PαI). In addition, the predominant form is IαI, a complex of HC1 and HC2 covalently bound to the CS chain of bikunin. Abbreviations: CS, chondroitin sulfate; HC, heavy chain; IαI, inter-α-trypsin inhibitor.