TABLE 2.

Ion channel residues that influence ferritin iron mineral dissolution and Fe²⁺ exit

Protein	Via (7% of mineral) (0–30 s)	Time of 25% mineral dissociation	Time of 50% mineral dissociation
	irons/min	min	min
Wild type	78 ± 8.2	43.0 ± 7.1b	>60.0b
R72D	77 ± 7.8	7.4 ± 1.0	17 ± 3.5
L134P	75 ± 7.3	7.0 ± 1.2	19 ± 3.8
D122R	63 ± 6.6	5.8 ± 0.8	12 ± 2.4c

^a Initial rates of Fe²⁺ exit can only be computed for the first 30 s, when the progress curve is linear; only 7% of the Fe²⁺ iron exits during this period. Changing ferritin cage ion channel structure has no effect on the initial rate; such iron probably represents iron bound in the protein cage rather than dissolved from the bulk mineral. Mineral dissolution, a surface-limited process, and Fe²⁺ exit continue for minutes to hours. Note that substitutions at other conserved channel residues, exemplified by Glu-130 and Asp-127, have no affect on Fe²⁺ exit (4).

^b Significantly slower (p < 0.01) than any of the ferritins with substitutions at conserved ion channel residues.

^c Fe²⁺ exit is significantly faster in M-D122R at 60 min than for M-R72D (p < 0.05) and M-L134P.