Table 1. Respiratory-chain complex activities in 143B, C4T, C9T and rho° cells.

Enzymic activities were measured in isolated mitochondria prepared from each cell line as described in the Experimental section. Values are expressed in nmol of substrate (donor or acceptor) consumed·min⁻¹·(mg of protein)⁻¹. Assays were performed on two or three different mitochondrial preparations. Mean values are shown with the range in parentheses, and mean ratios comparing complex activities are also shown. Activities are not normalized with respect to citrate synthase activity.

Enzyme activities	143B cells	C4T cells	C9T cells	rho° cells
Complex I	26	0.3	0.9	∼0
	(24–28), n=2	(0–0.5), n=2	(0–1.4), n=3	n=2
Succinate dehydrogenase	48	21	35	22
	(40–63), n=3	(19–23), n=2	(21–43), n=3	(17–27), n=2
Complex II	105	40	99	40
	(77–128), n=3	(37–42), n=3	(85–107), n=3	(35–43), n=3
Complex II+III	71	32	75	∼0
	(67–78), n=3	(27–41), n=3	(57–93), n=3	(0–1.6), n=3
Complex III	354	399	426	∼0
	(251–469), n=3	(286–513), n=3	(321–485), n=3	(0–3.7), n=3
Complex IV	251	180	311	∼0
	(219–287), n=3	(157–208), n=3	(280–336), n=3	(0–2.6), n=3
Citrate synthase	302	343	376	292
	(241–354), n=3	(292–425), n=3	(346–392), n=3	(205–365), n=3
Ratios
I/II+III	0.37	0.01	0.01
I/III	0.07	0.001	0.002
I/IV	0.10	0.002	0.003
II/III	0.30	0.10	0.23
II/IV	0.42	0.22	0.32
III/IV	1.41	2.22	1.37
IV/II+III	3.54	5.63	4.15