Human leucocyte elastase (HLE) preferentially cleaves the heavy chain H2 of inter-alpha-trypsin inhibitor (ITI)

Abstract

Inter-alpha-trypsin inhibitor (ITI) is a complex protein containing two heavy polypeptide chains (H1 and H2) 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 H1 and H2, and (iii) their N-terminal sequences. Our results demonstrate that the H2 heavy chain of ITI is particularly sensitive to HLE, and that early cleavage products (M(r)-values 120-150,000) consist of H1 linked to bikunin. A scheme is proposed for the mechanism for ITI degradation.