title: Ascaris suum cytochrome b5, an adult-specific secretory protein reducing oxygen-avid ferric hemoglobin.
abstract: The anaerobic parasitic nematode Ascaris suum has an oxygen-avid hemoglobin in the perienteric fluid, the biological function of which remains elusive. Here, we report that Ascaris cytochrome b5 is expressed specifically in the intestinal parasitic stage and is secreted into the perienteric fluid, thus co-localizing with Ascaris hemoglobin. We also found that cytochrome b5 reduces Ascaris non-functioning ferric methemoglobin more efficiently than mammalian methemoglobin. Furthermore, a computer graphics model of the electron transfer complex between Ascaris cytochrome b5 and Ascaris hemoglobin strongly suggested that these two proteins are physiological redox partners. Nitric oxide has been reported to react easily with oxygen captured in hemoglobin to form nitrate, but not toxic free radicals, which may result in production of methemoglobin for the cytochrome b5 to regenerate functional ferrous hemoglobin. Therefore, our findings suggest that Ascaris cytochrome b5 is a key redox partner of Ascaris hemoglobin, which acts as an antioxidant.
authors.affiliation: Department of Molecular and Cellular Parasitology, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan.
authors.forename: Muneaki
authors.initials: M
authors.lastname: Hashimoto
authors.forename: Shinzaburo
authors.initials: S
authors.lastname: Takamiya
authors.forename: Takehiro
authors.initials: T
authors.lastname: Yokota
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Nakajima
authors.forename: Fumiyuki
authors.initials: F
authors.lastname: Yamakura
authors.forename: Shigetoshi
authors.initials: S
authors.lastname: Sugio
authors.forename: Takashi
authors.initials: T
authors.lastname: Aoki
mesh_terms: D000693:Anaerobiosis; D000818:Animals; D017165:Ascaris suum / Q000201:enzymology* / Q000254:growth & development*; D001826:Body Fluids / Q000201:enzymology; D015786:Cytochromes b5 / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D005290:Ferric Compounds / Q000378:metabolism*; D005296:Ferrous Compounds / Q000378:metabolism; D006801:Humans; D008706:Methemoglobin / Q000378:metabolism*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D008706:Methemoglobin; D015786:Cytochromes b5; D010100:Oxygen