Table 3.

Association constants K_adetermined for the interaction of alanine mutants of BPTI with bovine β-trypsin and α-chymotrypsin at pH 8.2 and 5.5, 22°C

	Trypsin			Chymotrypsin
BPTI mutant	Ka (M−1) pH 5.5	Ka (M−1) pH 8.2	effect	Ka (M−1) pH 5.5	Ka (M−1) pH 8.2	effect
R15	—	4.5 × 1013a	—	1.27 × 107	2.5 × 108	—
A13R15	7.2 × 109	4.5 × 1011	1.0 × 102 ↓	1.22 × 107	2.4 × 108	1
A11A13R15	6.0 × 109	4.2 × 1011	1.1 × 102 ↓	1.15 × 107	2.2 × 108	1.1 ↓
R15A17	4.1 × 1011	2.8 × 1013b	1.6 ↓	—	1.8 × 108	1.4 ↓
R15A34	6.5 × 1011	4.4 × 1013b	1.0	—	2.2 × 108	1.1 ↓
R15A34A37A30	7.4 × 108	5.2 × 1010	8.7 × 102 ↓	—	6.0 × 106	41.7 ↓
A13R15A17A18A19	5.9 × 108	4.0 × 1010b	1.1 × 103 ↓	—	1.5 × 106	1.7 × 102 ↓
A11A13R15A17A18A19	6.1 × 108	4.1 × 1010b	1.1 × 103 ↓	—	3.7 × 106	67.6 ↓
A13 R15A17A18A19A34	3.5 × 106	2.4 × 108b	1.9 × 105 ↓	—	2.0 × 105	1.3 × 103 ↓
A11A13R15A17A18A19A34	3.6 × 106	2.4 × 108b	1.9 × 105 ↓	—	3.7 × 106	67.6 ↓
A11A13R15A17A18A19A34A37A39	5.1 × 104	3.4 × 106b	1.3 × 107 ↓	3.4 × 104	6.6 × 105a	3.8 × 102 ↓

Inhibition effects were compared with the pseudo wild-type BPTI. Downward arrow indicates a decrease in the association constant value upon mutations. Estimated error of K_a values is ±20%.

^a From Krowarsch et al. (1999).

^bK_a values calculated from the equation K_{a,pH 8.2} = K_{a,pH 5.5} × 68 (see text).

^cK_a values calculated from the equation K_{a,pH 8.2} = K_{a,pH 5.5} × 19.5 (see text).