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 two heavy polypeptide chains (H-1 and H-2) and a light chain, which in the free state is known as bikunin. In vitro cleavage of ITI with different 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 behavior, (ii) their immunological reactivity towards antibodies specific for each of the heavy chains H-1 and H-2, and (iii) their N-terminal sequences. Our results demonstrate that the H-2 heavy chain of ITI is particularly sensitive to HLE, and that early cleavage products (M(r)-values 120-150000) consist of H-1 linked to bikunin. A scheme is proposed for the mechanism for ITI degradation.