Trypsin inhibitors in guinea pig plasma: isolation and characterization of contrapsin and two isoforms of alpha-1-antiproteinase and acute phase response of four major trypsin inhibitors.

Contrapsin and two isoforms, F (fast) and S (slow), of alpha-1-antiproteinase (also called alpha-1-proteinase inhibitor) were isolated in an apparently homogeneous state from plasma of inflamed guinea pigs. Contrapsin inactivated trypsin, but did not significantly affect chymotrypsin, pancreatic elastase, or pancreatic kallikrein. On the other hand, both isoforms of alpha-1-antiproteinase inhibited trypsin, chymotrypsin, and elastase, but not plasma or pancreatic kallikrein. The S isoform of alpha-1-antiproteinase was present in barely detectable amounts in healthy animals, but increased markedly when the acute-phase reaction was induced by subcutaneous injection of turpentine. On the other hand, the plasma levels of the F isoform, contrapsin, and alpha-macroglobulin showed moderate (1.5 to 2.3-fold) elevation during the acute-phase reaction. In contrast to the previous findings that rats and rabbits contain two different alpha-macroglobulins, one of which is an acute-phase reactant while the other is not, inflamed guinea pigs contained only one species of alpha-macroglobulin. Murinoglobulin, the most prominent acute-phase negative protein in both mice and rats, showed no significant change in guinea pigs. These results indicate that guinea pig plasma contains four major trypsin inhibitors, i.e., contrapsin, alpha-1-antiproteinase, alpha-macroglobulin, and murinoglobulin, the properties of which are very similar to those of the respective mouse homologues, but that the acute-phase response of these inhibitors differs greatly from that of the homologous proteins in rats or mice.