Analysis of the plasma elimination kinetics and conformational stabilities of native, proteinase-complexed, and reactive site cleaved serpins: comparison of alpha 1-proteinase inhibitor, alpha 1-antichymotrypsin, antithrombin III, alpha 2-antiplasmin, angiotensinogen, and ovalbumin

Biochemistry. 1991 Feb 12;30(6):1723-30. doi: 10.1021/bi00220a039.


Proteinase inhibitors of the serpin superfamily may exist in one of three distinct conformations: the native form, a fully active protein with the reactive site loop intact; the proteolytically modified form in which inhibitory capacity is abolished; and the proteinase-complexed form, a stable equimolar complex between the inhibitor and a target proteinase. Here, the specificity and kinetics of the plasma elimination of different serpin conformations are compared. Proteinase-complexed serpins were rapidly cleared from the circulation. However, the native and modified forms were not cleared rapidly, indicating that the receptor-mediated pathways which recognize the complexes fail to recognize the native and modified forms. This result suggests that significant structural differences exist between modified and proteinase-complexed serpins. The structural differences were probed by using transverse urea gradient gel electrophoresis, a technique that allows comparisons of the conformational stabilities of proteins. With the exception of the noninhibitory serpins ovalbumin and angiotensinogen, the modified and proteinase-complexed serpins were both stabilized thermodynamically compared to the native forms. In addition, the proteinase component of the serpin-proteinase complex was usually thermodynamically stabilized. These data are used to compare the conformations of serpin-proteinase complexes with those of native and modified serpins; they are discussed in terms of a model whereby serpins inhibit proteinases in a manner similar to that described for other types of protein inhibitors of serine proteinases.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Angiotensinogen / metabolism*
  • Animals
  • Antithrombin III / metabolism*
  • Binding Sites
  • Drug Stability
  • Fibrinolysin / metabolism*
  • Kinetics
  • Molecular Sequence Data
  • Ovalbumin / metabolism*
  • Protein Binding
  • Protein Conformation
  • Sequence Homology, Nucleic Acid
  • Serine Endopeptidases / metabolism*
  • Serpins / chemistry
  • Serpins / metabolism*
  • alpha 1-Antichymotrypsin / metabolism*
  • alpha 1-Antitrypsin / metabolism*
  • alpha-Macroglobulins / metabolism*


  • Serpins
  • alpha 1-Antichymotrypsin
  • alpha 1-Antitrypsin
  • alpha-Macroglobulins
  • plasmin-alpha(2)-macroglobulin complex
  • Angiotensinogen
  • Antithrombin III
  • Ovalbumin
  • Serine Endopeptidases
  • Fibrinolysin