PLANT FERRITIN INTERACTION WITH THE CELLULAR CATALYTICALLY ACTIVE FE

GALATRO A; ROBELLO E; PUNTARULO S

Buenos Aires, Argentina

Workshop; Workshop Oxidative Stress and Antioxidants; 2009

Ferritin (Ft) plays a dual role in the homeostasis of the cellular labile Fe pool (LIP). In Fe rich conditions it acts as Fe sequestering protein, protecting plant cells against Fe toxicity, and at low Fe conditions it acts as a source of Fe ions. The main objective of the present study was to characterize the Fe uptake from isolated soybean Ft. Embryonic axes isolated from soybean seeds incubated for 24 h yielded 5-7 mg Ft  g-1 FW. Subunits analyses of the protein by SDS-polyacrilamide gel electrophoresis indicated that the protein was composed by 28 kDa protein subunits, confirmed by immunoblotting; however, a lower molecular mass subunits could appear. Since the absolute nature of the cellular LIP is not clear, the rate of in vitro incorporation of Fe into Ft was tested by supplementing the reaction medium with physiological Fe chelators. The control rate observed in the presence of 100 mM Fe chelated to Tris/HCl buffer (Fe/Ft  ratio 1000:1)  was not affected by the exposure to 100 mM Fe-Histidine (1:5); however, it was significantly increased by the addition of 100 mM Fe-citrate (1:2) (approximately 3.7-fold) or of 100 mM Fe-ATP (1:2) (approximately 2.5-fold). Moreover, a substantial decrease in the content of Trp in the Ft protein was determined during Fe uptake from Fe-citrate, as compared to control (10-fold), suggesting a drastic lost of protein stability. The data presented here suggest that Ft ability to modulate the LIP, not only depends upon Fe cellular content but also on the composition of the LIP. Supported by grants from the University of Buenos Aires and CONICET.