Table 2.

Function and homology of fdhF and hyc gene products

FHL subunit	Molecular mass (kDa)	Function in FHL	Hyf subunit	Nuo complex I subunit (E. coli)	Thermus thermophilus
FDH-H (fdhF gene)	79.12	Formate oxidation	Unknown	NuoG (C terminus)	Nqo3
HycA	17.59	Transcriptional regulator
HycB	21.80	FDH-H small subunit	HyfA	NuoG (N terminus)	Nqo3
HycC	63.98	Transmembrane subunit (16 TMH)a	HyfB	NuoL	Nqo12
		Transmembrane subunit (14 TMH)	HyfD, HyfF	NuoM/N	Nqo13-14
HycD	32.97	Transmembrane subunit (8 TMH), coupling site	HyfC	NuoH	Nqo8
HycE (1–150 aa)		Hydrogenase large subunit	HyfG	NuoC	Nqo5
HycE (150–569 aa)	64.89 (61.06)b	Hydrogenase large subunit, [NiFe] cofactor	HyfG	NuoD	Nqo4
HycF	20.27	Electron transfer subunit	HyfH	NuoI	Nqo9
HycG	27.95	Hydrogenase small subunit, FeS/N2-cluster	HyfI	NuoB	Nqo6
HycH	15.43	Large subunit chaperone, not essential for FHL activity	HyfJ
HycI	16.99	Endoprotease	Unknown	Not required	Not required
		Transmembrane protein	HyfE (C terminus)	NuoK	Nqo11
		Transcriptional regulator, similar to FhlA	HyfR
		Putative formate channel	FocB

^a TMH, transmembrane α-helices.

^b Molecular mass after protein specific processing; mass given includes the first 150 amino acids (aa).