Table 1.

Kinetic and stoichiometric parameters for the proprotein  convertases

Enzyme	Coumarinamide substrate	Peptide-based inhibitor	Protein-based inhibitor
	pERTKR-MCA Km, μM	Dec-RVKR-CH2Cl Ki, nM	α1-PIT/hf	α1-PDX/hf
			Ki, nM	Ki, nM	SI
Furin	4.7	2.0	>500	1.4	2¶
Furin/f†	3.2	0.60	>500	0.60§	2¶
PC6B/f†	0.41	0.11	>500	2.3§	8¶
PC3/f†	25	2.0	>500	260§	40¶
PC2	54	0.36	>500	1,000	nd
PACE-4/f†	6.3	3.6	>500	>5,000	nd
PC7/f†	19	0.12	>500	>5,000	nd
Thrombin	12‡	nd	0.05	>5,000	nd

Assays were performed in duplicate. Reported values are the mean of three independent experiments (SEM <15%). All PCs were active-site titrated with Dec-RVKR-CH₂Cl. Calculations assume α₁-PDX/hf, α₁-PIT/hf, and Dec-RVKR-CH₂Cl are fully active. SI values were determined as described in legend to Fig. 4. nd, not determined. 

^†Molecular mass determined by Western blot using mAb M2: Furin/f (86 kDa); PC6B/f [144 kDa (major band) and 60 kDa (minor band)]; PC3/f [86 kDa (major band) and 67 kDa (minor band)]; PACE-4/f (102 kDa); PC7/f (79 kDa). 

^‡Boc-D(Bz)-PR-MCA. 

^§EI* complex determined by Western blot; α₁-PDX/hf⋅furin/f (160 kDa); α₁-PDX/hf⋅PC6B/f (two bands corresponding to the 144- and 60-kDa forms); α₁-PDX/hf⋅PC3/f (two bands corresponding to the 86- and 67-kDa forms). 

^¶Cleaved α₁-PDX/hf (I*) detected on incubation with the respective enzyme.