Interaction of human alpha1-antichymotrypsin with chymotrypsin

Serine protease inhibitor activity of recombinant squamous cell carcinoma antigen towards chymotrypsin, as demonstrated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis

Squamous cell carcinoma (SCC) antigen was tested, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, for its ability to inhibit the activity of serine proteases, i.e., trypsin, chymotrypsin and elastase. We demonstrated that the serine protease inhibitor (serpin) of SCC antigen is specific for chymotrypsin. Preincubation of chymotrypsin with recombinant SCC antigen inhibited chymotryptic digestion of gelatin and ovalbumin through the formation of sodium dodecyl sulfate-stable complexes. These findings promote understanding of the biological functions of SCC antigen as serpin in the stratification of the normal squamous cells and in the malignant behavior of the tumor cells.

Studies on the interactions of human pancreatic elastase 2 with human alpha 1-proteinase inhibitor and alpha 1-antichymotrypsin

The interactions of human pancreatic elastase 2 with alpha 1-proteinase inhibitor and alpha 1-antichymotrypsin were compared by studies in vitro. The equimolar complexes obtained between the enzyme and either inhibitor were relatively stable at 25 degrees C since they could be visualized for up to 5 days by an electrophoretic method. However, in both cases, a slow dissociation occurred with release of active enzyme. As the kass. rate constants are of the same order of magnitude, with a slightly lower value for alpha 1-proteinase inhibitor when compared with alpha 1-antichymotrypsin [(5.6 +/- 1.2) X 10(5) and (8.9 +/- 1.3) X 10(5) M-1.s-1 respectively], partition of human pancreatic elastase 2 between both inhibitors in human plasma is mainly dependent on their respective concentrations. A comparative study by crossed immunoelectrophoresis of the interactions of this enzyme with the two inhibitors contained in normal human plasma and in a mimetic mixture of pure inhibitors was carried out. This allowed the visualization of complexes with either inhibitor. Formation of such a complex with alpha 1-antichymotrypsin had never been demonstrated previously. The patterns obtained are similar when working with normal plasma or with the synthetic mixture, suggesting that, in the conditions used, alpha 1-proteinase inhibitor and alpha 1-antichymotrypsin are the main inhibitors of human pancreatic elastase 2 in the plasma sample. However, it is also shown that part of the enzyme may be taken up by alpha 2-macroglobulin, which is responsible for the remaining enzyme activity on a synthetic substrate. The present work suggests that, according to the delay times of inhibition of human pancreatic elastase 2 calculated from the normal plasma concentrations of alpha 1-proteinase inhibitor and alpha 1-antichymotrypsin, a significant role can be assigned to both inhibitors. Moreover, the role of alpha 1-antichymotrypsin would be enhanced in alpha 1-proteinase-inhibitor deficiency.

Kinetics of interaction of C1 inhibitor with complement C1s

The kinetics of inhibition of the complement serine protease, C1s, by its only known inhibitor, C1 inhibitor, have been measured by a variety of methods. One method continuously monitors the loss of esterolytic activity with a synthetic substrate coupled to a chromogen while another monitors the formation of a stable (covalent) complex by high-pressure size-exclusion chromatography under dissociating conditions. Additional methods employ fluorescence probes to follow the formation of bimolecular complexes but are not expected to distinguish between covalent product and noncovalent (reversible) intermediates. There was good agreement between rate constants obtained by the various methods over a broad range of inhibitor concentrations, suggesting that noncovalent intermediates do not accumulate to a significant extent. The reaction appears to be pure second order with a bimolecular rate constant of 6.0 X 10(4) M-1 s-1 at 30 degrees C, independent of Ca2+, and an activation energy of 11.0 kcal/mol. The rate increases up to 35-fold in the presence of heparin which was shown to bind to all three components (enzyme, inhibitor, and complex) with similar affinity (Kd = 2.0-3.3 microM). The fluorescent probe 1,1'-bis(anilino)-4-,4'-bi(naphthalene)-8,8'-disulfonate [bis(ANS)] bound to the complex with Kd = 0.26 microM under conditions where the individual components had little affinity for the dye, consistent with the generation of one or more hydrophobic binding sites on the protein surface during complex formation.

Human serum alpha 1-antichymotrypsin is an inhibitor of pancreatic elastases

Incubation of human serum alpha 1-antichymotrypsin with human pancreatic elastase 2 or porcine pancreatic elastase results in the complete inhibition of each enzyme as determined by spectrophotometric assays. alpha 1-Antichymotrypsin reacts much more rapidly with the human than with the porcine enzyme. The inhibitor: enzyme molar ratio, required to obtain full inhibition of enzymatic activity, is equal to 1.25/1 when alpha 1-antichymotrypsin reacts with human pancreatic elastase 2 while it is markedly higher with porcine pancreatic elastase (5.5/1). Patterns obtained by SDS/polyacrylamide gel electrophoresis of the reaction products show the formation with both enzymes of an equimolar complex (Mr near 77 000) and the release of a fragment migrating as a peptide of Mr near 5000. Moreover a free proteolytically modified form of alpha 1-antichymotrypsin, electrophoretically identical with that obtained in the reaction with cathepsin G or bovine chymotrypsin, is produced in the reaction with each elastase but in a much greater amount when alpha 1-antichymotrypsin reacts with porcine elastase than with human elastase. As a consequence of our findings, the specificity of alpha 1-antichymotrypsin, so far limited to the inhibition of chymotrypsin-like enzymes from pancreas and leukocyte origin, has to be extended to the two pancreatic elastases investigated in this work. A contribution of alpha 1-antichymotrypsin to the regulatory balance between plasma inhibitors and human pancreatic elastase 2 in pancreatic diseases is suggested.