TABLE 3.

Kinetic constants and stoichiometries of inhibition for the reactions of serpin B8, α₁PDX, and α₁PDX-serpin B8 chimeras with furin and furin alanine loop mutants

Values of k_a and SI ±S.E. for serpin-furin reactions were measured at pH 7.5, 25 °C as in Table 1. SIs for the reactions of α₁PDX-serpin B8 P6–P5′-YE chimera with the furin loop mutants could not be determined because of enzyme instability over the long times required for complete reaction.

Furin surface loop variant	Serpin B8		α1PDX		α1PDX-serpin B8 P6–P1		α1PDX-serpin B8 P1′–P5′		α1PDX-serpin B8 P6–P5′		α1PDX-YE		α1PDX-serpin B8 P6–P5′-YE
	ka	SI	ka	SI	ka	SI	ka	SI	ka	SI	ka	SI	ka	SI
	m−1 s−1		m−1 s−1		m−1 s−1		m−1 s−1		m−1 s−1		m−1 s−1		m−1 s−1
Wild-type	2.4 ± 0.3 × 105	1.5 ± 0.1	1.1 ± 0.1 × 106	1.1 ± 0.1	2.5 ± 0.3 × 106	1.3 ± 0.1	5.5 ± 0.8 × 104	1.2 ± 0.1	1.1 ± 0.1 × 105	1.4 ± 0.1	2.1 ± 0.3 × 105	1.9 ± 0.1	1.5 ± 0.2 × 103	1.3 ± 0.2
187–189	5.6 ± 0.9 × 104	1.2 ± 0.2	3.8 ± 0.8 × 105	0.9 ± 0.1	3.5 ± 0.3 × 105	1.3 ± 0.1	2.0 ± 0.3 × 104	1.0 ± 0.0	2.5 ± 1.0 × 104	1.5 ± 0.1	4.2 ± 0.7 × 104	1.0 ± 0.1	5.5 ± 0.4 × 102	NDa
298–300	6.1 ± 1.3 × 104	1.5 ± 0.3	1.8 ± 0.1 × 106	1.2 ± 0.1	2.7 ± 0.3 × 106	1.4 ± 0.0	2.3 ± 0.2 × 104	1.0 ± 0.0	1.9 ± 0.9 × 104	1.0 ± 0.1	1.3 ± 0.1 × 105	0.8 ± 0.2	1.5 ± 0.1 × 103	ND
345–350	1.5 ± 0.2 × 105	1.1 ± 0.1	5.2 ± 0.5 × 105	1	6.7 ± 0.9 × 105	1.0 ± 0.1	4.7 ± 1.1 × 104	1.1 ± 0.2	8.9 ± 1.7 × 104	1.8 ± 0.1	1.7 ± 0.3 × 105	1.3 ± 0.1	1.4 ± 0.0 × 103	ND
357–359	5.6 ± 1.1 × 104	1.3 ± 0.2	7.1 ± 1.0 × 105	0.8 ± 0.1	8.5 ± 0.9 × 105	1.0 ± 0.0	5.2 ± 1.1 × 104	0.9 ± 0.1	7.4 ± 1.9 × 104	1.3 ± 0.1	6.9 ± 1.0 × 104	0.8 ± 0.2	1.0 ± 0.2 × 103	ND

^a ND, not determined.