TABLE 1.

Specificity and activity of the inhibitors used in this study

Inhibitor	Abbreviation	Specificity	Reference	Concentration	% inhibition of degradationa
Brefeldin A	BFA	Vesicle transport	23, 24	5 μg/ml	ND
Lactacystin	LC	Proteasome	25, 26	10 μm	ND
Leupeptin	LEU	Trypsin-like proteases and cysteine proteases	28	100 μm	38 ± 18
Pepstatin	PEP	Aspartic proteases	28, 29	100 μm	50 ± 5
1,10-Phenanthroline	PHE	Metalloproteases and caspase-1	29, 30	50 μm	ND
E64	E64	Cysteine proteases C1	31	100 μm	ND
Puromycin	PUR	Dipeptidyl-peptidase II and PSA	61	0.5 μg/ml	ND
Captopril	CAP	ACE and ACE-like proteases	29	100 μm	25 ± 2
Benzyl succinyl acid	BEN	Metallo-carboxypeptidases A and B	29	100 μm	−10 ± 8
Bestatin	BES	Most of metallo-aminopeptidases	29	50 μm	ND
Phosphoramidon	PHO	All bacterial metallo-endopeptidases but few of mammalian origin	29, 62	100 μm	15 ± 4
Leucine thiol	LeuSH	Metallo-aminopeptidases including ERAP	57	30 μm	ND
Benzyloxycarbonyl-VAD-fluoromethyl ketone	Z-VAD-fmk	Caspases	63	100 μm	NDb

^a Activity of these inhibitors was measured as their ability to prevent proteolytic degradation in cellular extracts as in Ref. 15. The amount of protein still present after incubation in the case of the degraded control sample was considered 0% inhibition of degradation, and the nondegraded sample was taken as 100% inhibition. Data are means of two independent experiments. Negative values indicate that there was enhanced degradation in the presence of the compound. ND indicates not done.

^b The compound was found to block apoptosis (data not shown).