HUMAN-LEUKOCYTE ELASTASE (HLE) PREFERENTIALLY CLEAVES THE HEAVY CHAIN-H-2 OF INTER-ALPHA-TRYPSIN INHIBITOR (ITI)

Inter-alpha-trypsin inhibitor (ITI) is a complex protein containing tw o heavy polypeptide chains (H-1 and H-2) and a light chain, which in t he free state is known as bikunin. In vitro cleavage of ITI with diffe rent proteases releases bikunin, but does not abolish the antitryptic activity. To study the mechanism of bikunin release, ITI was incubated with human leucocyte elastase (HLE). The resulting ITI fragments were characterized by (i) their electrophoretic and chromatographic behavi or, (ii) their immunological reactivity towards antibodies specific fo r each of the heavy chains H-1 and H-2, and (iii) their N-terminal seq uences. Our results demonstrate that the H-2 heavy chain of ITI is par ticularly sensitive to HLE, and that early cleavage products (M(r)-val ues 120-150000) consist of H-1 linked to bikunin. A scheme is proposed for the mechanism for ITI degradation.