TABLE 1.

Enzymes involved in autotrophic CO₂ assimilation in T. neutrophilus^a

Enzymee	Assay temp (°C)b	Sp act (nmol min−1 mg of protein−1) in cells grown with the following cosubstratec:					Gene(s)d
		None	Acetate	4-OH- butyrate	Succinate	Pyruvate
Pyruvate synthase (oxidized methyl viologen)	65	190	400	330	200	60	Tneu_1795/Tneu_1796/Tneu_1797
Fumarate hydratase	65	500	<10	<10	<10	<10	Tneu_1334/Tneu_1335
Fumarate reductase (reduced methyl viologen)	65	130	<10	<10	<10	<10	Tneu_0423/Tneu_0424
Succinyl-CoA synthetase	65	280	20	20	120	80	Tneu_1463/Tneu_1464
Succinyl-CoA reductase (NADPH)	65	260	20	10	100	60	Tneu_0421
Succinic semialdehyde reductase (NADPH)	65	7,000	900	1,300	3,200	1,000	Tneu_0419
4-Hydroxybutyrate-CoA ligase	85	670	110	140	230	170	Tneu_0420
4-Hydroxybutyryl-CoA dehydratase	85	200	<10	20	90	40	Tneu_0422

^aExtracts from cells grown with CO₂ as the sole carbon source were compared with extracts from cells grown with CO₂ and another organic carbon source as the cosubstrate. The energy source was H₂ plus S⁰ in all cases.

^bBecause of the use of mesophilic coupling enzymes and the instability of some substrates, the indicated assay temperatures were used; the growth temperature was 85°C.

^cThe generation times were 8 h with no substrate, 3 h with acetate, and 5 h with 4-hydroxybutyrate (4-OH-butyrate), succinate, or pyruvate. Values are means from at least duplicate determinations using several separately prepared extracts from different batches of cells. The maximal deviations are approximately 20%.

^dSubunits of multicomponent enzymes are separated by slashes.

^eThe electron carrier used is given in parentheses.