Dual mitochondrial localization and different roles of the reversible reaction of mammalian ferrochelatase

Abstract

Ferrochelatase catalyzes the insertion of ferrous ions into protoporphyrin IX to produce heme. Previously, it was found that this enzyme also participates in the reverse reaction of iron removal from heme. To clarify the role of the reverse reaction of ferrochelatase in cells, mouse liver mitochondria were fractionated to examine the localization of ferrochelatase, and it was found that the enzyme localizes not only to the inner membrane, but also to the outer membrane. Observations by immunoelectron microscopy confirmed the dual localization of ferrochelatase in ferrochelatase-expressing human embryonic kidney cells and mouse liver mitochondria. The conventional (zinc-insertion) activities of the enzyme in the inner and outer membranes were similar, whereas the iron-removal activity was high in the outer membrane. 2D gel analysis revealed that two types of the enzyme with different isoelectric points were present in mitochondria, and the acidic form, which was enriched in the outer membrane, was found to be phosphorylated. Mutation of human ferrochelatase showed that serine residues at positions 130 and 303 were phosphorylated, and serine at position 130 may be involved in the balance of the reversible catalytic reaction. When mouse erythroleukemia cells were treated with 12-O-tetradecanoyl-phorbol 13-acetate, an activator of protein kinase C, or hemin, phospho-ferrochelatase levels increased, with a concomitant decrease in zinc-insertion activity and a slight increase in iron-removal activity. These results suggest that ferrochelatase localizes to both the mitochondrial outer and inner membranes and that the change in the equilibrium position of the forward and reverse activities may be regulated by the phosphorylation of ferrochelatase.

Isolation and characterization of free haem from the shell gland of quail and hen

“…An abundance of haem in shell gland, as shown here for the first time, provides readily available substrate for biliverdin synthesis. It has been speculated (Wang et al , ) that protoporphyrin could be derived directly from haem by reversal of the ferrochelatase reaction, first demonstrated by Taketani et al (), and further characterized by him in mammalian tissue (Sakaino et al , ). Whether haem has a central role in the integrative control of eggshell pigmentation as the precursor not only of biliverdin but also of protoporphyrin remains to be defined, but there is no evidence, despite 90 years of conjecture (Giersberg, ), that the haem originates from circulating erythrocytes.…”

One ring to rule them all: Trafficking of heme and heme synthesis intermediates in the metazoans

“…As noted above, five pathway proteins possess either organic co-factors or essential metals. To date no pathway enzymes has been shown to be glycosylated and only mouse liver FECH has been reported to be phosphorylated [52], albeit on residues that that appear to be in inaccessible sites within the protein. Interestingly these investigators also reported that phosphorylated FECH is located on the mitochondrial outer membrane, something never reported by any other group previously.…”

Erythropoietin signaling regulates heme biosynthesis

“…PKC-mediated FECH phosphorylation occurs in a domain buried within an inaccessible hydrophobic fold that did not directly impact enzyme catalysis (Sakaino et al, 2009). In contrast, the position of Thr116 (Thr115 in mice) that is modified by PKA suggests that it would have a direct effect on FECH activity (Wu et al, 2001).…”