Archives of Insect Biochemistry and Physiology 39:133–143 (1998) © 1998 Wiley-Liss, Inc. Uptake of Rhodnius Heme-Binding Protein (RHBP) by the Ovary Of Rhodnius prolixus Ednildo A. Machado, 1 Pedro L. Oliveira, 1 Monica F. Moreira, 1 Wanderley de Souza, 2 and Hatisaburo Masuda 1 * 1 Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Rio de Janeiro, Brasil 2 Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brasil The uptake of RHBP (Rhodnius heme-binding protein) by the ovaries of Rhodnius prolixus was characterized. RHBP puri- fied from oocyte was labeled with 125 I and used to study the process of uptake by the ovary in vivo and in vitro. After injec- tion, the [ 125 I]RHBP was readily removed from the hemolymph and accumulated especially in the ovary. The capacity of the ovary to take up [ 125 I]RHBP from the hemolymph varied dur- ing the days following blood meal. It increased up to day 2, remained stable until day 5, and then decreased up to the end of oogenesis. In vitro, the uptake of [ 125 I]RHBP was linear at least up to 60 min. The uptake was dependent on [ 125 I]RHBP concentration and showed to be a saturable process. The addi- tion of a molar excess of non-related proteins such as Vitellin (Vt), Lipophorin (Lp), and Bovine Serum Albumin (BSA) did not reduce [ 125 I]RHBP uptake. Using immunogold technique the RHBP was localized at the microvilli, coated pits, and yolk gran- ules. The main yolk protein, Vt, did not compete with RHBP for the uptake. Thus, it is discussed here that they bind to in- dependent binding sites of the oocytes, and are directed later on to the same compartment. The need of both proteins for the completion of mature oocyte was verified in vivo. The reduc- tion of heme-RHBP in the hemolymph, by changing the diet, decreased the number of eggs laid. Increasing the concentra- tion of heme-RHBP in the hemolymph, the number of eggs pro- duced increased in a dose dependent manner. In vitro, both apo-RHBP and heme-RHBP can be taken up by the oocyte. Since the mature oocyte contains only heme-saturated RHBP, the possible fate of apo-RHBP is also discussed. Arch. Insect Biochem. Physiol. 39:133–143, 1998. © 1998 Wiley-Liss, Inc. *Abbreviations used: apo-RHBP = RHBP free of heme; BSA = Bovine Serum Albumin; heme-RHBP = RHBP associated with heme; [ 125 I]RHBP = 125 I – labeled RHBP; Lp = lipop- horin; Mvg = microvitellogenin; PBS = phosphate buffered saline; RCBP = Rhodnius calcium-binding protein; rRHBP = reconstituted heme-RHBP; RHBP = Rhodnius heme-bind- ing protein; Vg = vitellogenin; Vt = vitellin. Contract grant sponsor: Conselho Nacional de Desen- volvimento Científico e Tecnológico (CNPq); Contract grant sponsor: Financiadora de Estudos e Projetos (FINEP); Con- tract grant sponsor: Programa De Apoio ao Desenvolvimento Científico e Tecnológico (PADCT); Contract grant sponsor: Programa de Núcleos de Excelência (PRONEX). *Correspondence to: Hatisaburo Masuda, Universidade Fed- eral do Rio de Janeiro, Instituto de Ciências Biomédicas, Departamento de Bioquímica Médica, Cidade Universitária - Ilha do Fundão, 21.944-590, Rio de Janeiro, RJ, Brasil. E- mail: masuda@server.bioqmed.ufrj.br Received 4 May 1998; accepted 25 September 1998