Table 7.

Effect of the YE Exosite Residues on PC Reactivity with α1PDX and the α1PDX-serpin B8 RCL P6-P5’ Chimera

α1PDX-Serpin B8 Chimera	Second order association rate, ka(M−1s−1)
	FURIN	PC4	PC5	PACE4	PC7
P6-P5’	1.1 ± 0.1 × 105	7.1 ± 1.0 × 102	6.0 ± 0.2 × 102	2.9 ± 0.1 × 102	7.7 ± 2.2 × 102
P6-PS’+YE exosites	1.5 ± 0.2 × 103	9.1 ± 0.1 × 101	6.9 ± 0.4 × 101	8.1 ± 0.2 × 101	2.2 ± 0.1 × 101
α1PDX	1.1 ± 0.1 × 106	1.6 ± 0.3 × 106	2.0 ± 0.1 × 106	1.2 ± 0.3 × 106	2.3 ± 0.8 × 106
α1PDX+YE exosites	2.1 ± 0.3 × 105	1.4 ± 0.4 × 107	8.6 ± 2.9 × 106	4.4 ± 1.0 × 106	6.7 ± 2.0 × 106

The tyrosine (Y) and glutamic acid (E) exosite residues were grafted at their homologous location in strand 3 of sheet C of α1PDX and the P6-P5’ chimera. Serpin B8 has the conserved residue phenylalanine at the position of the tyrosine residue. Second order association rate constant (k_a) values for the reaction of PCs with the chimeras α1PDX+YE exosites and the α1PDX-serpin B8 RCL P6-P5’+YE exosites were determined as described in Table 3. Errors represent S.E from linear regression fits of data. The ka values for the reaction of furin with both chimeras were taken from reference (10). The ka values for the reaction of α1PDX and the P6-P5’ chimera with all PCs were taken from tables 2 and 3 and included for comparison.