Table 3.

Dissociation Constants of Transition State Analogues with HsPNP and His²⁵⁷ Mutants

	DADMe-ImmH			ImmH				5′-deoxy-ImmH
	Ki*a	Km/Ki		Ki	Ki*	Km/Ki		Kib	Km/Ki
Enzyme		Value	Fold			Value	Fold		Value	Fold
Native	10.7 ± 1.1 pM	3,700,000	1	a	57.9 ± 1.5 pM	690,000	1	20.0 ± 0.9 nM	2,000	1
His257Phe	950 ± 60 pM	337,000	11	172 ± 16 nM	b	1,860	370	19.8 ± 1.0 nM	16,200	8
His257Gly	270 ± 20 pM	2,800,000	1	11.0 ± 0.9 nM	b	68,100	10	7.7 ± 0.6 nM	97,000	93
His257Asp	900 ± 100 pM	1,500,000	2	86 ± 7 nM	b	15,700	45	54 ± 3 nM	25,000	12

^aThe weak inhibition phase (K_i) was observed but too short to quantitate, so only the slow-onset, tight-binding phase (K_i*) is reported.

^bNo slow-onset phase was observed.