Human Cationic and Anionic Trypsins: Differences of Interaction with α1Proteinase Inhibitor

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Abstract
Human cationic (trypsin 1) anionic (trypsin 2) trypsins were obtained by controlled activation of purified trypsinogens 1 and 2, respectively. The interactions of trypsin 1 and trypsin 2 with human .alpha.1-proteinase inhibitor (.alpha.1PI) were analysed and compared by studies in vitro. The enzymatic activity and inhibitory capacity measurements were assessed using Glp-Gly-Arg-Nan as substrate. The association rate constants showed that the inhibition of trypsin 2 occurred more than 10 times faster than that of trypsin 1. The equimolar complexes obtained between either trypsin and .alpha.1PI were visualized by electrophoresis followed by immunoblotting inhibition of the two trypsins was temporary i.e. the complexes trypsin 1-.alpha.1PI and trypsin 2-.alpha.1PI broke down with time yielding inactive .alpha.1PI (Mr 50,000) and active enzyme. But the stability time for trypsin 1-.alpha.1PI was much larger than that of trypsin 2-.alpha.1PI. In vivo, .alpha.1PI is not able to control the activity of trypsin 1 except when .alpha.2-macroglobulin (.alpha.2M) is already saturated. According to the day times of inhibition calculated from normal concentrations in serum, .alpha.1PI inhibits trypsin 2 as fast as .alpha.2M inhibits trypsin 1. These results suggest that a significant role can be assigned to .alpha.1PI in the inhibition of trypsin 2 in physiological conditions and of trypsin 1 in pathological ones.

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