Binding interactions of β-conglycinin and glycinin with vitamin B12

Vitamin B12 deficiency is a problem for many elderly people around the world that is caused by food-cobalamin malabsorption syndrome due to gastrointestinal problems. In this study, the molecular interactions of VB12 with two major soy protein fractions, β-conglycinin (7S) and glycinin (11S), were studied using fluorescence and far-UV circular dichroism spectroscopic techniques. The results show that the fluorescence of 7S and 11S was quenched by VB12 through binding-related quenching after correcting for the inner-filter effect. Both 7S and 11S had a good affinity to VB12 as indicated by their high binding constant 1.252 (±0.085) × 10(4) M(-1) for 7S and 0.952 (±0.04) × 10(4) M(-1) for 11S at 292 K, respectively. Such binding induced a more organized protein confirmation with increased β-sheet and β-turn structure components and a more folded tertiary structure. It is deduced that VB12 was bound in the interior of protein three-dimensional network mainly via hydrophobic interactions to form 7S-VB12 and 11S-VB12 complexes. The results suggest that soy protein has potential to be used as carrier of VB12.