TABLE 1.

Characterization of the PL and SMP preparations

The values reported in rows 1, 2, and 4 are in μmol NADH min⁻¹ (mg of protein)⁻¹. The respiratory control ratio (RCR, row 3) is a qualitative measure of how well the particles are coupled, but it depends also on the catalytic activity, the enzyme concentration in the membrane, and the ability of an enzyme to work against Δp. In independent measurements on SMPs, ATP hydrolysis displayed an RCR value of only 1.6 but was shown to support a Δp of more than 0.15 V (23). “Oriented complex I” is complex I with its NADH-binding site exposed to the external solution. The values reported in row 7 are in μmol NADH min⁻¹ (mg of complex I)⁻¹). Comparison of the values for BtPLs and BtSMPs shows that the CI in SMPs is around twice as active as that in PLs. However, the activity in BtPLs is commensurate with values from the most active preparations of BtCI (16,58). The difference probably arises from the nonphysiological quinone analogue required for the BtPLs and from the harsh procedure for preparing BtPLs (solubilization and chromatography in detergent-containing solutions and reconstitution into an artificial membrane) relative to BtSMPs (sonication and centrifugation steps that retain the native membrane). Our SMPs are comparable in size with those of Li et al. (59) (∼100 nm), and the value given for their total internal volume (in μl (mg of protein)⁻¹) is a representative value based on that of Sorgato et al. (60) (1.3 μl (mg of protein)⁻¹) and an equivalent value determined for this preparation using the same protocol (0.83 ± 0.12 μl (mg of protein)⁻¹); the value is similar to values determined for inverted bacterial membrane vesicles using an EPR spin probe (1 μl (mg of protein)⁻¹) (8, 9). The numbers of oriented complex I per particle are average values calculated from rows 5, 6, 8, and 9 by considering a uniform set of spherical particles, membrane thickness of 5 nm, and a uniform distribution of complex I.

	PLs		SMPs (B. taurus)
	B. taurus	Y. lipolytica
NADH:DQ or O2 oxidoreduction	0.90 ± 0.04	0.46 ± 0.03	0.25 ± 0.01 (23)
Row 1 with gramicidin	2.39 ± 0.19	1.70 ± 0.04	0.74 ± 0.02 (23)
RCR value (row 2/row 1)	2.66 ± 0.24	3.70 ± 0.26	3.02 ± 0.15
Row 2 with piericidin A	0.13 ± 0.03	0.055 ± 0.01	0.05 ± 0.02
Fraction of oriented complex I	0.55 ± 0.03	0.48 ± 0.03	0.81 ± 0.05 (23)
Fraction of protein that is complex I	0.95 ± 0.01	∼1	∼0.096 (23)
Row 2 corrected for rows 6 and 5	4.57 ± 0.48	3.54 ± 0.24	9.55 ± 0.70
Particle radius (nm)	143 ± 12	129 ± 4	163 ± 25
Total internal volume	22.8 ± 4.4	21.0 ± 6.2	∼1.0
Oriented complex I per particle	140	100	700