TABLE 5.

Solubilization of iron(III) reductase from whole cells of G. sulfurreducens^a

Addition(s)b	Fraction	Protein (mg)	Iron(III) reductase activityc with:
			NADH			Horse heart cytochrome c
			Sp act (mU/mg of protein)	Total activity (mU)	Soluble fraction/cell ratio (%)	Sp act (mU/mg of protein)	Total activity (mU)	Soluble fraction/cell ratio (%)
None	Soluble fraction	2.0 ± 0.2	0	0	0	0	0	0
	Cells	2.2 ± 0.1	16.6 ± 1.0	36.5 ± 2.0	100	17.5 ± 3.0	38.5 ± 5.0	100
KCl	Soluble fraction	3.6 ± 0.2	2.1 ± 0.1	7.6 ± 0.2	34	4.4 ± 0.4	15.8 ± 1.0	54
	Cells	2.6 ± 0.1	5.7 ± 0.5	14.8 ± 2.0	66	5.1 ± 0.5	14.0 ± 2.0	46
EDTA	Soluble fraction	3.4 ± 0	0	0	0	0	0	0
	Cells	2.8 ± 0.4	11.7 ± 1.5	32.8 ± 4.0	100	9.5 ± 0.5	26.6 ± 1.0	100
KCl + EDTA	Soluble fraction	3.3 ± 0.2	6.4 ± 0.5	21.1 ± 1.0	66	11.7 ± 2.0	38.6 ± 4.0	81
	Cells	2.6 ± 0.1	4.2 ± 0.2	10.9 ± 0.5	34	3.4 ± 0.4	8.8 ± 1.0	19

^aFor solubilization experiments, cells were dissolved in 100 mM Tris buffer (pH 7.8). 

^bKCl was added to a final concentration of 0.5 M; EDTA was added to a final concentration of 1 mM. 

^cReactions 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.