Table 2.

Inhibition of SprP activity by protease inhibitors

Inhibitor	Specificity	Concentration (mmol/L)	Inhibition (%)
Control	–	–	0.0 ± 3.7
AEBSF	Serine protease	2	75.7 ± 1.9
TPCK	Serine protease	2	25.8 ± 3.1
EDTA	Metallo protease	7	0.0 ± 3.4
E-64	Cysteine protease	0.1	6.2 ± 2.0
Pepstatin A	Aspartyl protease	0.1	6.0 ± 1.1

SprP (3 μg) was incubated in 200 mmol/L Tris-HCl, 5 mmol/L CaCl₂, pH 8 buffer for 1 h at 4°C in the presence of the respective inhibitor. Protease activity was determined with resorufin-labeled casein as the substrate. The enzymatic activity of a control reaction without protease inhibitor was set as 100%. AEBSF, 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride; TPCK, N-p-tosyl-l-phenylalanine chloromethyl ketone; EDTA, ethylenediaminetetraacetic acid; E-64, N-(trans-epoxysuccinyl)-l-leucine 4-guanidinobutylamide; pepstatin A, Iva-Val-Val-Sta-Ala-Sta.