TABLE 2.
Localization of iron(III) reductase in different cellular fractions of G. sulfurreducens
| Fraction | Protein (mg) | Iron(III) reductase
activitya with:
|
|||||
|---|---|---|---|---|---|---|---|
| NADH
|
Horse heart cytochrome c
|
||||||
| Sp act (mU/mg of protein) | Total activity (mU) | % | Sp act (mU/mg of protein) | Total activity (mU) | % | ||
| Whole cells vs. crude extract | |||||||
| Whole cells | 110 ± 7 | 4.8 ± 0.2 | 528 ± 20 | 100 | 7.0 ± 0.7 | 770 ± 70 | 100 |
| Crude extract | 114 ± 10 | 7.7 ± 0.5 | 878 ± 50 | 166 | 7.4 ± 0.5 | 844 ± 50 | 110 |
| Periplasm vs. spheroplasts | |||||||
| Periplasm | 1.7 ± 0.2 | 9 ± 1 | 15.3 ± 2 | 23 | 9.5 ± 1 | 16.2 ± 2 | 32 |
| Spheroplasts | 8.7 ± 1.0 | 6.0 ± 1 | 52.0 ± 9 | 77 | 4.0 ± 0.5 | 35.0 ± 4 | 68 |
| Soluble fraction vs. membrane fraction | |||||||
| Soluble fraction | 7.5 ± 1 | 9.7 ± 0.5 | 72.7 ± 5 | 17 | 11.0 ± 1 | 82 ± 7.0 | 33 |
| Membrane fraction | 60.3 ± 0.5 | 6.0 ± 1 | 362 ± 6 | 83 | 2.7 ± 0.5 | 163 ± 3 | 67 |
a
Reactions were performed in 50 mM HEPES buffer (pH 7) containing 0.3 mM Fe(III)-NTA, 0.5 mM ferrozine, and either 1 mM NADH or 4 μM horse heart cytochrome c. An activity of 1 mU corresponds to 1 nmol of Fe(II) formed per min.