The mitochondrial localization of coproporphyrinogen III oxidase

Abstract

The location of coproporphyrinogen III oxidase in mitochondria was studied in rat liver by using the digitonin method or hypo-osmotic media for fractionation. The enzyme was found in the intermembrane space with a fraction loosely bound to the inner membrane. This fraction was released by washing the inner-membrane-matrix complex with alkaline solutions or solutions of high ionic strength. The enzyme in both fractions had the same Km (0.16 micrometer) for coproporphyrinogen III. When incubation was performed in a medium that avoided destruction of enzyme membrane binding, a dramatic increase in activity was observed after sonication of whole mitochondria or of the inner-membrane-matrix complex.

The mitochondrial location of protoporphyrinogen oxidase

“…The significant decrease in the synthesis of protoporphyrin IX from coproporphyrinogen I11 when mitochondria are treated in a way that induces leakage of coproporphyrinogen oxidase from the intermembrane space further emphasizes the functional importance of the location of coproporphyrinogen oxidase in the vicinity of protoporphyrinogen oxidase: since in these tests protoporphyrinogen formation was not decreased, the delay in the appearance of protoporphyrin observed with hypoosmotically treated mitochondria may be due to a deficient transfer of protoporphyrinogen to the mitochondrial inner membrane: these results strengthen the hypothesis that coproporphyrinogen oxidase acts as a shuttle in the intermembrane space for the transfer of protoporphyrinogen to the inner membrane [2].…”

“…l), indicating that the access of protoporphyrinogen to the catalytic center of protoporphyrinogen oxidase does not involve an energy-dependent transport mechanism but that the lipophilicity of protoporphyrinogen allows this substrate to diffuse passively within the lipid layer of the membrane. This process may even be facilitated if protoporphyrinogen is synthesized by coproporphyrinogen oxidase in close contact with the inner membrane as previously suggested [2]. Uptake of protoporphyrin IX was reported to occur in intact mitochondria by an energy-dependent process [I 51.…”

Purification and properties of mouse liver coproporphyrinogen oxidase

“…Mouse liver coproporphyrinogen oxidase was activated by phospholipids and neutral detergents, as described for the bovine and yeast enzymes. This supports the view that the enzyme may interact with the mitochondrial inner membrane during heme biosynthesis in vivo, as postulated by Grandchamp et al [5] and Deybach et al [24]. The mechanism of activation by phospholipids may be closely related to that observed for the bovine liver enzyme since both V,,, (Table 3) and K, values for the enzymes are changed in the presence of phospholipids.…”

Two novel mutations and coexistence of the 991C.T and the 1339C.T mutation on a single allele in the coproporphyrinogen oxidase gene in Swedish patients with hereditary coproporphyria

“…(Anderson et al 2001). This mitochondrial enzyme (Grandchamp et al 1978) operates as a homodimer (Kohno et al 1993) and catalyzes the conversion of coproporphyrinogen III to protoporphyrinogen IX in the sixth step of heme biosynthesis (Dailey 1997).…”