TABLE 3.

Kinetic parameters for H-II and H-I from P. furiosus

Hydrogenase	Substratea (mM)	Cosubstratea (mM)	Apparent Km (mM)	kcat (min−1)	kcat/Km (min−1 mM−1)	kcat (I)/kcat (II)
H-II	MV+ (0–4.0)	DT (10.0) + H+ (10−5)	1.25 ± 0.2	6,400	5,120
H-II	MV2+ (0–4.0)	H2b	1.0 ± 0.2	1,760	1,760
H-II	H2 (0–0.836)	MV2+ (1.0)	0.13 ± 0.01	960	7,385
H-II	NADPH (0–0.5)	H+ (10−5)	0.063 ± 0.004	24	381
H-II	NADH (0–0.5)	H+ (10−5)	0.071 ± 0.005	22	315
H-II	NADP (0–0.2)	H2b	0.017 ± 0.003	43	2,541
H-II	NAD (0–0.5)	H2b	0.125 ± 0.015	96	768
H-II	S0 (0.25–1.0%)e	H2b	0.2 ± 0.02c	41	NAd
H-II	PSe (0–3.0 mM)	NADPH (0.4 mM)	0.67 ± 0.10	10	15
H-I	MV+ (0–4.0)	DT (10.0) + H+ (10−5)	0.2 ± 0.02	42,900	214,500	6.7
H-I	MV2+ (0–10)	H2b	5.0	37,500	7,500	21.3
H-I	H2 (0–0.836)	MV2+ (1.0)	0.14	1,575	11,250	1.6
H-I	NADPH (0–2.0)	H+ (10−5)	0.2	1,500	7,500	62.5
H-I	NADH (0–8.0)	H+ (10−5)	3.0	240	80	11
H-I	NADP (0–0.4)	H2b	0.04	11,250	281,000	262
H-I	NAD (0–1.0)	H2b	NA	0	NA	NA
H-I	S0 (1–5%)e	H2b	1.8 ± 0.2e	1,665	NA	4.5
H-I	PSe (0–3.0 mM)	NADPH (0.4 mM)	2.0 ± 0.2	390	195	38

^aAbbreviations: MV, methyl viologen; DT, sodium dithionite; Fd, ferredoxin. 

^bPure H₂ gas was used at a pressure of 120 kPa. 

^cTaken from reference 17. 

^dNA, not applicable. 

^eThe concentration of S⁰ is expressed as percent (weight/volume), not a millimolar concentration. PS, polysulfide.