Heme crystallization in the midgut of triatomine insects.

Hemozoin (Hz) is a heme crystal produced by several blood-feeding organisms in order to detoxify free heme released upon hemoglobin (Hb) digestion. Here we show that heme crystallization also occurs in three species of triatomine insects. Ultraviolet-visible and infrared light absorption spectra of insoluble pigments isolated from the midgut of three triatomine species Triatoma infestans, Dipetalogaster maximus and Panstrongylus megistus indicated that all produce Hz. Morphological analysis of T. infestans and D. maximus midguts revealed the close association of Hz crystals to perimicrovillar membranes and also as multicrystalline assemblies, forming nearly spherical structures. Heme crystallization was promoted by isolated perimicrovillar membranes from all three species of triatomine bugs in vitro in heat-sensitive reactions. In conclusion, the data presented here indicate that Hz formation is an ancestral adaptation of Triatominae to a blood-sucking habit and that the presence of perimicrovillar membranes plays a central role in this process.

A new intracellular pathway of haem detoxification in the midgut of the cattle tick Boophilus microplus: aggregation inside a specialized organelle, the hemosome.

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.