Characterization of Fe distribution in soybean seeds and Fe uptake by ferritin.

GALATRO A; ROBELLO E; PUNTARULO S

Los Cocos, Córdoba

Congreso; XXXVIII Reunión Annual de la Sociedad Argentina de Biofísica; 2009

Fe is an essential element for the growth and well-being of almost all living organisms involved in many biological functions. The Fe exceeding the metabolic needs of the cell may form a low molecular weight pool (labile Fe pool, LIP), which catalyzed the conversion of normal by-products of cell respiration, like superoxide anion and hydrogen peroxide, into highly damaging hydroxyl radical or into equally aggressive ferryl ions or oxygen-bridgedFe2+/Fe3+ complexes. Ferritins (Ft), which have the ability to sequester several thousand of Fe atoms in their central cavity in a soluble, nontoxic bioavailable form, play a key role in preventing Fe toxicity. The main objective of the present study was to characterize Fe metabolism in soybean embryonic axes, and the Fe uptake from isolated soybean Ft. Embryonic axes isolated from soybean seeds incubated for 24 h showed an Fe reduction rate of 15 ± 1 nmol Fe3+ min-1 mg-1 DW, a total Fe content of 1.3 ± 0.2 nmol Fe mg-1 DW, and a LIP content of 30 ± 13 pmol mg-1 DW. The content of Ft, isolated from seeds incubated for 24 h, was 34 ± 11 mg Ft g-1 DW with 1054 ± 111 Fe atoms molecule-1. Analyses of the protein by SDS-polyacrilamide gel electrophoresis indicated that the protein was composed by a 28 kDa protein subunit, confirmed by immunoblotting. The rate of in vitro Fe uptake into Ft was tested by supplementing the reaction medium with physiological Fe chelators. The control rate observed in the presence of Fe chelated to Tris/HCl buffer (Fe:Ft ratio, 1000:1) was significantly increased by the addition of Fe-citrate (1:2) (approximately 3.7-fold) or Fe-ATP (1:2) (approximately 2.5-fold). In addition, a significant decrease in tryptophane content in the Ft was observed during Fe uptake from Fe-citrate, as compared to Fe chelated to buffer (10-fold), suggesting an important lost of protein stability. The data presented here suggest that in soybean seeds, non-heme Fe is mainly distributed into the LIP and the Ft, under physiological conditions. Moreover, the interaction Ft:LIP could be modulated by the nature of the cellular chelators available to conform the LIP.