TABLE 1.

Relative kinetic parameters of mutant FIV PRs with fluorogenic substrates

Proteasea	FIV FSb			HIV FSc
	Km (μM)	Kcat (min−1)	Kcat/Km	Km (μM)	Kcat (min−1)	Kcat/Km
Wild-type FIV	20.4 ± 1.8	3.01 ± 0.11	0.147	—d	—	—
Mutants
37/55/56/59	8.7 ± 0.4	0.89 ± 0.02	0.102	—	—	—
55/56/59/99	30.2 ± 2.2	1.32 ± 0.03	0.044	—	—	—
37/55/56/59/99	35.9 ± 1.9	1.33 ± 0.05	0.037	—	—	—
37/55/56/59/98/99	38.3 ± 3.2	2.25 ± 0.08	0.059	—	—	—
F9s	12.4 ± 0.6	0.53 ± 0.02	0.043	96.1 ± 17.7	0.05 ± 0.005	0.0005
Wild-type HIV-1	8 ± 2	0.026 ± 0.006	0.003	2.2 ± 0.7	0.9 ± 0.2	0.4

^a37,137³²V; N55⁴⁶M; 56,M56⁴⁷I; 59,V59⁵⁰I; 98,198⁸¹P; 99,Q99⁸²V. The equivalent HIV numbering is in superscript. F9s: 137³²V/N55⁴⁶M/M56⁴⁷I/V59⁵⁰I/L97⁸⁰T/198⁸¹P/Q99⁸²V/P100⁸³N/L101⁸⁴I.

^bFIV FS, fluorogenic substrate derived from the FIV CA/NC2 cleavage junction (ALTKVQ*VVQSKG).

^cHIV FS, fluorogenic substrate derived from the HIV-1 P2/NC cleavage junction (TIM*MQR).

^d—, no detectable activity in this assay.