Lupin ferritin: Purification and characterization, biosynthesis and regulation of in vitro synthesis in plant system

Ferritin from lupin seedlings was isolated and purified to homogeneity. Identification was performed by iron-specific staining, determination of physico-chemical properties and electron microscopy. The molecular weight of lupen ferritin under native conditions was about 500 kDa; this protein consists of three subunits (MW: 28 kDa, 26.5 kDa and 22.5 kDa). The biosynthesis of lupen ferritin has been tested ≪in vivo≫ in roots of lupen seedlings and in the ≪in vitro≫ translation system of wheat germ. During in vitro and in vivo biosynthesis ferritin is synthesized as a dominant 31 kDa or 28 kDa polypeptide, respectively. The transcriptional mechanism of ferritin biosynthesis regulation is supported by observation of higher syntheses of this protein by poly A +RNA isolated from lupin growing on FeSO 4 (in comparison to control — water conditions). Addition of the 22.5 kDa subunit to the in vitro translation system of wheat germ causes a reduction of ferritin syntheses whereas the 28 kDa subunit has no effect, This observation suggests the parallel existence of an autoregulatory mechanism of ferritin biosynthesis at the translational level.