title: Catabolism of hemoglobin-haptoglobin complex in microsome subfractions.
abstract: After internalization of hemoglobin-haptoglobin complex (Hb-Hp) via receptor-mediated endocytosis (RME) into liver parenchymal cells, organelles containing the complex distribute in the microsome fraction (Ms). Prior to the catabolism, Hb-Hp dissociates symmetrically into two 82,000-dalton (82 kDa) subunits. In the present investigation, the first event of Hb-Hp metabolism in Ms were further examined after [3H-heme, 14C-glogin]Hb-Ho or [125I-Hb]Hp injection to rats. Shortly after the internalization of Hb-Hp, this complex in Ms was intact. At 60 min after injection, radioactive materials of Ms extracted by freezing and thawing (F&T) with yield of 15% were composed of Hb-Hp, 82 kilodaltons (kDa) subunits and Hb metabolites with a ratio of 1:6:13. The heme metabolites were identified as [3H]bilirubin by high performance liquid chromatography (HPLC). The ratio of Hb-Hp/82 kDa subunits/Hb metabolites in microsome residue of the F&T was 40:8:1. The radioactivity in Ms at 60 min localized microsomes subfraction except Golgi light fraction. In electron microscope radioautography of microsome subfraction using [125I]Hb-Hp, silver grains were observed over or within morphologically heterogenous vesicles, e.g. vesicles containing very low density lipoprotein (VLDL) particles with appendage like multi-vesicular body (MVB) or compartment of uncoupling of receptor and ligand (CURL) in Goligi light and intermediate fractions. These studies suggest that Hb-Hp internalized by RME is dissociated symmetrically into two 82 kDa subunits in organelles of Ms, and that organelles with MVB or CURL-like structures are associated with Hb-Hp metabolism.
authors.affiliation: Department of Biochemical Genetics, Tokyo Medical and Dental University, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Oshiro
authors.forename: Y
authors.initials: Y
authors.lastname: Yajima
authors.forename: K
authors.initials: K
authors.lastname: Kawamura
authors.forename: M
authors.initials: M
authors.lastname: Kubota
authors.forename: J
authors.initials: J
authors.lastname: Yokofujita
authors.forename: Y
authors.initials: Y
authors.lastname: Nishibe
authors.forename: M
authors.initials: M
authors.lastname: Takahama
authors.forename: H
authors.initials: H
authors.lastname: Nakajima
mesh_terms: D000818:Animals; D002850:Chromatography, Gel; D006242:Haptoglobins / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism; D008862:Microsomes, Liver / Q000378:metabolism*; D051381:Rats
chemical_list: D006242:Haptoglobins; D006454:Hemoglobins