Iron loading into ferritin by an intracellular ferroxidase

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Medicine

Background:

• Cellular iron uptake and storage are critical physiological processes.
• Ferritin is the primary intracellular iron-storage protein.
• The mechanisms of iron transport and loading into ferritin are not fully elucidated.

Purpose of the Study:

• To isolate and characterize a membrane-bound enzyme with ferroxidase activity from horse heart plasma membranes.
• To investigate the enzyme's role in catalyzing iron loading into ferritin.
• To compare the properties of this tissue ferroxidase with serum ceruloplasmin.

Main Methods:

• Isolation of plasma membrane fraction from horse heart.
• Assay of p-phenylenediamine oxidase and ferrous iron oxidase activities.
• Measurement of iron loading into apoferritin.
• Inhibition studies using anti-horse serum ceruloplasmin antibody.
• Stoichiometric analysis of iron oxidation and oxygen consumption.

Main Results:

• An intracellular, membrane-bound enzyme with both p-phenylenediamine oxidase and ferroxidase activities was identified.
• The tissue ferroxidase activity was stimulated by apoferritin, leading to iron loading into ferritin.
• Anti-horse serum ceruloplasmin antibody inhibited the iron loading process.
• The stoichiometry of iron oxidation and oxygen consumption was similar to that of serum ceruloplasmin.

Conclusions:

• A ferroxidase analogous to ceruloplasmin is present on the plasma membrane of horse heart.
• This membrane-bound ferroxidase catalyzes the loading of iron into ferritin.
• The findings suggest a novel mechanism for cellular iron uptake and storage, impacting current models.