TABLE 2.

Cleavage of fluorescent substrates designed for HIV-1 PR and FIV PR^a

PR	Substrate	Mean Km (μM) ± SD	Mean kcat (s−1) ± SD	Mean kcat/Km (μM−1 s−1)
HIV-1	HIV-1b	2.2 ± 0.7	0.9 ± 0.2	0.4
HIV-1	FIVc	8 ± 2	0.026 ± 0.006	0.003
FIV	FIV	13 ± 5	0.11 ± 0.02	0.008
FIV	HIV-1	NDd	ND	NAe

^aCleavage reactions were conducted at pH 5.6 in 0.2 M NaCl–0.1 M MES at 37°C with 368 nM FIV PR or 297 nM HIV-1 PR. 

^bAbz-Thr-Ile-Nle↓Phe(NO₂)-Gln-Arg-NH₂ (26). 

^cNH₂-Arg-Ala-Leu-Thr-Lys-(Abz)-Val-Gln↓Phe-(NO₂)-Val-Gln-Ser-Lys-Gly-Arg-NH₂ (9). 

^dND, cleavage of the HIV-1 PR substrate by FIV PR was undetectable after 1 h by fluorescence increase or HPLC. 

^eNA, not applicable.