Table 1.
Observed association rate constants (kobs) between human trypsins and wild-type or Pittsburgh mutant α1-antitrypsin (α1AT). PRSS1, cationic trypsin; PRSS2, anionic trypsin; PRSS3, mesotrypsin; R198G, mesotrypsin mutant Arg198→Gly. Rate constants were determined from three independent measurements, using a discontinuous or continuous assay, as described in Experimental Procedures. The errors of curve fits are indicated. To obtain the true second order association rate constants, the kobs values need to be multiplied with the stoichiometry of inhibition (SI). With the exception of mesotrypsin, the SI was approximately unity, therefore kobs equals ka. Mesotrypsin associates with α1AT Pittsburgh with an SI of 2, and the calculated ka is 1.1 × 106 M−1 s−1. N. D., not determined. Using purified pancreatic cationic and anionic trypsins and native wild-type α1AT, Vercaigne-Marko et al. (1989) reported association rate constants of 1.35 x 104 M−1 s−1and 1.8 x 105 M−1 s−1, respectively [12].
|
kobs M−1 s−1 |
||
|---|---|---|
| α1AT | α1AT Pittsburgh | |
| PRSS1 | 8.7 ± 0.2 × 103 | 2.3 ± 0.1 × 106 |
| PRSS2 | 1.6 ± 0.1 × 105 | 2.0 ± 0.1 × 106 |
| PRSS3 | N.D. | 5.4 ± 0.3 × 105 |
| R198G | 3.3 ± 0.2 × 104 | 2.2 ± 0.1 × 106 |