The delivery of therapeutic proteins is one of the greatest challenges in the treatment of human diseases. In this frame, ferritins occupy a very special place. Thanks to their hollow spherical structure, they are used as modular nanocages for the delivery of anticancer drugs. More recently, the possibility of encapsulating even small proteins with enzymatic or cytotoxic activity is emerging. Among all ferritins, particular interest is paid to the Archaeoglobus fulgidus one, due to its peculiar ability to associate/dissociate in physiological conditions. This protein has also been engineered to allow recognition of human receptors and used in vitro for the delivery of cytotoxic proteins with extremely promising results.

Escherichia coli flavohemoglobin (HMP) is shown to be capable of catalyzing the reduction of several alkylhydroperoxide substrates into their corresponding alcohols using NADH as an electron donor. In particular, HMP possesses a high catalytic activity and a low K_m toward cumyl, linoleic acid, and tert-butyl hydroperoxides, whereas it is a less efficient hydrogen peroxide scavenger. An analysis of UV-visible spectra during the stationary state reveals that at variance with classical peroxidases, HMP turns over in the ferrous state. In particular, an iron oxygen adduct intermediate whose spectrum is similar to that reported for the oxo-ferryl derivative in peroxidases (Compound II), has been identified during the catalysis of hydrogen peroxide reduction. This finding suggests that hydroperoxide cleavage occurs upon direct binding of a peroxide oxygen atom to the ferrous heme iron. Competitive inhibition of the alkylhydroperoxide reductase activity by carbon monoxide has also been observed, thus confirming that heme iron is directly involved in the catalytic mechanism of hydroperoxide reduction. The alkylhydroperoxide reductase activity taken together with the unique lipid binding properties of HMP suggests that this protein is most likely involved in the repair of the lipid membrane oxidative damage generated during oxidative/nitrosative stress.