title: A new intracellular pathway of haem detoxification in the midgut of the cattle tick Boophilus microplus: aggregation inside a specialized organelle, the hemosome.
abstract: The hard tick Boophilus microplus ingests large volumes of cattle blood, as much as 100 times its own mass before feeding. Huge amounts of haem are produced during haemoglobin digestion, which takes place inside acidic lysosomal-type vacuoles of the digest cells of the midgut. Haem is a promoter of free radical formation, so haemoglobin digestion poses an intense oxidative challenge to this animal. In the present study we followed the fate of the haem derived from haemoglobin hydrolysis in the digest cells of the midgut of fully engorged tick females. The tick does not synthesize haem, so during the initial phase of blood digestion, absorption is the major route taken by the haem, which is transferred from the digest cells to the tick haemocoel. After this absorptive period of a few days, most of the haem produced upon haemoglobin degradation is accumulated in the interior of a specialized, membrane-delimited, organelle of the digest cell, herein called hemosome. Haem accounts for 90% of the hemosome mass and is concentrated in the core of this structure, appearing as a compact, non-crystalline aggregate of iron protoporphyrin IX without covalent modifications. The unusual FTIR spectrum of this aggregate suggests that lateral propionate chains are involved in the association of haem molecules with other components of the hemosome, which it is proposed is a major haem detoxification mechanism in this blood-sucking arthropod.
authors.affiliation: Departamento de Bioquímica Médica, ICB, Universidade Federal do Rio de Janeiro, IMPPG, Universidade Federal do Rio de Janeiro, Brazil.
authors.forename: Flavio Alves
authors.initials: FA
authors.lastname: Lara
authors.forename: Ulysses
authors.initials: U
authors.lastname: Lins
authors.forename: Gabriela
authors.initials: G
authors.lastname: Paiva-Silva
authors.forename: Igor C
authors.initials: IC
authors.lastname: Almeida
authors.forename: Cláudia M
authors.initials: CM
authors.lastname: Braga
authors.forename: Flávio C
authors.initials: FC
authors.lastname: Miguens
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Oliveira
authors.forename: Marílvia
authors.initials: M
authors.lastname: Dansa-Petretski
mesh_terms: D000818:Animals; D001769:Blood / Q000378:metabolism; D002417:Cattle; D004063:Digestion; D004064:Digestive System / Q000378:metabolism; D005260:Female; D006418:Heme / Q000378:metabolism*; D006790:Host-Parasite Interactions; D026863:Ixodidae / Q000378:metabolism* / Q000472:pathogenicity / Q000648:ultrastructure; D008854:Microscopy, Electron; D015388:Organelles / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D006418:Heme