Human inter-alpha-trypsin inhibitor (I alpha I) is a plasma proteinase inhibitor active against cathepsin G, leucocyte elastase, trypsin and chymotrypsin. It owes its broad inhibitory specificity to tandem Kunitz-type inhibitory domains within an N-terminal region. Sequence studies suggest that the reactive-centre residues critical for inhibition are methionine and arginine. Reaction of I alpha I with the arginine-modifying reagent butane-2,3-dione afforded partial loss of inhibitory activity against both cathepsin G and elastase but complete loss of activity against trypsin and chymotrypsin. Reaction of I alpha I with the methionine-modifying reagent cis-dichlorodiammineplatinum(II) resulted in partial loss of activity against cathepsin G and elastase but did not affect inhibition of either trypsin or chymotrypsin. Employment of both reagents eliminated inhibition of cathepsin G and elastase. These findings suggest that both cathepsin G and elastase are inhibited at either of the reactive centres of I alpha I. Trypsin and chymotrypsin, however, appear to be inhibited exclusively at the arginine reactive centre.
Modification of the tandem reactive centres of human inter-α-trypsin inhibitor with butanedione and cis-dichlorodiammineplatinum(II)
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M W Swaim, S V Pizzo; Modification of the tandem reactive centres of human inter-α-trypsin inhibitor with butanedione and cis-dichlorodiammineplatinum(II). Biochem J 15 August 1988; 254 (1): 171–178. doi: https://doi.org/10.1042/bj2540171
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