Isolation and characterization of a new phytoferritin from broad bean (Vicia faba) seed with higher stability compared to pea seed ferritin

Plant ferritin widely occurring in legume seeds represents a novel alternative dietary iron source for treatment of iron deficiency anemia. However, recent studies have shown that known plant ferritins such as SSF and PSF are unstable because they contain a higher amount of the H-1 subunit. Therefore, it is of special interest to explore a new plant ferritin with a lower amount of the H-1. In the present study, a new ferritin (BBSF) was purified from broad bean seeds by consecutive anion exchange and size exclusion chromatography to homogeneity. The apparent molecular mass of BBSF was found to be 560 kDa by native-PAGE analysis. N-terminal sequence, MALDI-TOF-MS. and SDS-PAGE analyses indicate that BBSF consists of H-1 and H-2 subunits with a H1/H-2 ratio of 1:6, and shares very high sequence identity with PSF. In contrast, the ratio of H-1 to H-2 in pea seed ferritin (PSF) is 1:2 and in soybean seed ferritin (SSF) is 1:1. Thus, this new protein has quite different subunit composition from PSF and SSF, which might affect its activity in iron uptake. As expected. PSF exhibits a higher catalyzing activity than BBSF, and the association rate of PSF is faster than BBSF upon high iron loading of the protein. More importantly, the stability of BBSF is much higher than that of PSF and SSF under the same experimental conditions, which is beneficial to its application for iron supplement. (C) 2012 Elsevier Ltd. All rights reserved.