Abstract
Lipophorin (Lp) is the main haemolymphatic lipoprotein in insects and transports lipids between different organs. In adult females, lipophorin delivers lipids to growing oocytes. In this study, the interaction of this lipoprotein with the ovaries of Rhodnius prolixus was characterised using an oocyte membrane preparation and purified radiolabelled Lp (125I-Lp). Lp-specific binding to the oocyte membrane reached equilibrium after 40-60 min and when 125I-Lp was incubated with increasing amounts of membrane protein, corresponding increases in Lp binding were observed. The specific binding of Lp to the membrane preparation was a saturable process, with a K(d) of 7.1 ± 0.9 x 10-8M and a maximal binding capacity of 430 ± 40 ng 125I-Lp/µg of membrane protein. The binding was calcium independent and pH sensitive, reaching its maximum at pH 5.2-5.7. Suramin inhibited the binding interaction between Lp and the oocyte membranes, which was completely abolished at 0.5 mM suramin. The oocyte membrane preparation from R. prolixus also showed binding to Lp from Manduca sexta. When Lp was fluorescently labelled and injected into vitellogenic females, the level of Lp-oocyte binding was much higher in females that were fed whole blood than in those fed blood plasma.
Highlights
As in all oviparous animals, oogenesis in insects is characterised by an accumulation of nutrients in the oocytes that are to be consumed during embryonic development
Lp (125I-Lp) binding capacities of oocyte and fat body were compared and Fig. 1 shows that the specific binding of Lp to the oocyte membrane was much higher than to the fat body membrane; which was similar to the values previously described (Pontes et al 2002)
The binding of 125I-Lp to the different fractions produced during the oocyte membrane preparation was evaluated
Summary
As in all oviparous animals, oogenesis in insects is characterised by an accumulation of nutrients in the oocytes that are to be consumed during embryonic development. As previously described for the membrane preparations from the M. sexta midgut and R. prolixus fat body and midgut (Gondim & Wells 2000, Pontes et al 2002, Grillo et al 2003), 125I-Lp had the highest binding capacity to the final pellet, which was produced after centrifugation at 100,000 g (data not shown).
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