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Title
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Interaction of human alpha 1-proteinase inhibitor with chymotrypsinogen A and crystallization of a proteolytically modified alpha 1-proteinase inhibitor.
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Authors
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H.Löbermann,
F.Lottspeich,
W.Bode,
R.Huber.
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Ref.
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Hoppe Seylers Z Physiol Chem, 1982,
363,
1377-1388.
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PubMed id
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Abstract
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Human alpha 1-proteinase inhibitor (alpha 1-PI) can form very stable complexes
with chymotrypsinogen A or chymotrypsin if limited proteolysis by a contaminant
proteinase is prevented with diisopropyl fluorophosphate. The contaminant
proteinase cleaves the alpha 1-PI component in the alpha 1-PI-chymotrypsinogen A
complex close to its N-terminus, between threonine-11 and aspartate-12 and the
chymotrypsinogen A part between tyrosine-146 and threonine-147. By this
modification the complex becomes unstable and dissociates into modified alpha
1-PI and neo-chymotrypsinogen A. A tritium labelling experiment shows that the
contaminant proteinase is present in a 0.5-1.0% (w/w) ratio in the inhibitor
preparation. These experiments indicate that alpha 1-PI is not a temporary
inhibitor for these enzymes, as assumed by other authors. Isolated modified
alpha 1-PI can be crystallized as tetragonal bipyramides from 2.6M sodium
potassium phosphate pH 8.0. The crystals are suitable for three dimensional
X-ray structure analysis. In spite of the cleavage of the susceptible peptide
bond by chymotrypsinogen A, the C-terminal 3.6 kDa cleavage peptide remains
tightly bound to the inhibitor by means of non-covalent interactions. In
accordance with the result of the known complete amino-acid sequence of the
inhibitor this finding offers an alternative explanation to the suggestion of
alpha 1-PI being a double headed inhibitor. Isolated neo-chymotrypsinogen A can
be activated to active chymotrypsin and can form a very labile 1 : 1 complex
with alpha 1-PI, which dissociates rapidly into inactive inhibitor and
neo-chymotrypsinogen.
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