Table 3. K_i values (M) for R₄R₁-eglin containing the indicated substitution at position 49.

Residue at position 49*	Kex2	Furin	PC7
Tyr	9.1 × 10-10†	2.5 × 10-9†	1.3 × 10-9
Ala	1.0 × 10-9	1.8 × 10-9	2.9 × 10-9
Asp	5.6 × 10-11	3.3 × 10-10	1.8 × 10-9
Glu	3.6 × 10-11	5.3 × 10-10	2.9 × 10-9
Ser	2.1 × 10-10	4.8 × 10-9	2.5 × 10-9
Trp	1.2 × 10-9	1.0 × 10-8	4.7 × 10-10
Met	1.0 × 10-9	1.6 × 10-9	1.4 × 10-9

All values were determined by using purified inhibitors as described in Materials and Methods. Experimental errors were ±20%

^*In the context of R₄R₁-eglin

^†K_i values for Tyr-49-R₄R₁-eglin with Kex2 and furin are from ref. 11