Binding of aquocobalamin to bovine casein and its peptides via coordination to histidine residues

TY - JOUR

T1 - Binding of aquocobalamin to bovine casein and its peptides via coordination to histidine residues

AU - Fedosov, Sergey

AU - Nexø, Ebba

AU - Heegaard, Christian Würtz

PY - 2018/1

Y1 - 2018/1

N2 - Vitamin B 12 (cobalamin, Cbl) is an essential nutrient of bovine milk, bound to the casein fraction and the Cbl-specific protein transcobalamin at a ratio of 50:50. This study aimed to elucidate the mechanism of interaction between Cbl and the caseins. It was found that the isolated caseins bind aquocobalamin (HOCbl) via histidine-[Co 3+]Cbl coordination. The casein–Cbl complex slowly dissociated in the presence of KCN due to formation of CNCbl. The “active” His groups (5.7 mM measured in 41.6 mg mL −1 casein) accumulate ≤ 3 mM HOCbl at a high rate (t ½ ≈ 10 min, 20 °C) and with a high affinity (K d = 0.1 mM). Low pH hinders the binding, but does not accelerate a very slow dissociation (t ½ ≈ 8 h). Increased temperature and/or the presence of the specific Cbl-binding proteins accelerate the dissociation. The consequences of casein–Cbl interactions for the intestinal uptake of Cbl remain unclear.

AB - Vitamin B 12 (cobalamin, Cbl) is an essential nutrient of bovine milk, bound to the casein fraction and the Cbl-specific protein transcobalamin at a ratio of 50:50. This study aimed to elucidate the mechanism of interaction between Cbl and the caseins. It was found that the isolated caseins bind aquocobalamin (HOCbl) via histidine-[Co 3+]Cbl coordination. The casein–Cbl complex slowly dissociated in the presence of KCN due to formation of CNCbl. The “active” His groups (5.7 mM measured in 41.6 mg mL −1 casein) accumulate ≤ 3 mM HOCbl at a high rate (t ½ ≈ 10 min, 20 °C) and with a high affinity (K d = 0.1 mM). Low pH hinders the binding, but does not accelerate a very slow dissociation (t ½ ≈ 8 h). Increased temperature and/or the presence of the specific Cbl-binding proteins accelerate the dissociation. The consequences of casein–Cbl interactions for the intestinal uptake of Cbl remain unclear.

U2 - 10.1016/j.idairyj.2017.08.005

DO - 10.1016/j.idairyj.2017.08.005

M3 - Journal article

SN - 0958-6946

VL - 76

SP - 30

EP - 39

JO - International Dairy Journal

JF - International Dairy Journal

ER -